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1

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

2012-10-01

2

Habitable zone limits for dry planets.  

PubMed

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

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

2011-06-01

3

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

4

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

5

HYDROGEN GREENHOUSE PLANETS BEYOND THE HABITABLE ZONE  

SciTech Connect

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

Pierrehumbert, Raymond [Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637 (United States); Gaidos, Eric, E-mail: rtp1@geosci.uchicago.edu, E-mail: gaidos@hawaii.edu [Department of Geology and Geophysics, University of Hawaii at Manoa, Honoulu, HI 96822 (United States)

2011-06-10

6

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

7

What Can The Habitable Zone Gallery Do for You?  

NASA Astrophysics Data System (ADS)

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

Gelino, Dawn M.; Kane, Stephen R.

2014-06-01

8

Comparable Habitable Zones of Stars - Duration: 0:25.  

NASA Video Gallery

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

9

CANDIDATE PLANETS IN THE HABITABLE ZONES OF KEPLER STARS  

SciTech Connect

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

Gaidos, Eric, E-mail: gaidos@hawaii.edu [Department of Geology and Geophysics, University of Hawai'i at Manoa, Honolulu, HI 96822 (United States)

2013-06-20

10

The 55 Cancri System: Fundamental Stellar Parameters, Habitable Zone Planet, and Super-Earth Diameter  

E-print Network

The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. We use the CHARA Array to directly determine the following of 55 Cnc's stellar astrophysical parameters: $R=0.943 \\pm 0.010 R_{\\odot}$, $T_{\\rm EFF} = 5196 \\pm 24$ K. Planet 55 Cnc f ($M \\sin i = 0.155 M_{Jupiter}$) spends the majority of the duration of its elliptical orbit in the circumstellar habitable zone (0.67--1.32 AU) where, with moderate greenhouse heating, it could harbor liquid water. Our determination of 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e ($\\simeq 2.1 R_{\\earth}$), which, depending on the assumed literature value of planetary mass, implies a bulk density of 0.76 $\\rho_{\\earth}$ or 1.07 $\\rho_{\\earth}$.

von Braun, K; Brummelaar, T A ten; van Belle, G T; Kane, S R; Ciardi, D R; Lopez-Morales, M; McAlister, H A; Schaefer, G; Ridgway, S T; Sturmann, L; Sturmann, J; White, R; Turner, N H; Farrington, C; Goldfinger, P J

2011-01-01

11

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

12

The Habitable Zones of Pre-main-sequence Stars  

NASA Astrophysics Data System (ADS)

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

Ramirez, Ramses M.; Kaltenegger, Lisa

2014-12-01

13

The Habitable Zones of Pre-Main-Sequence Stars  

E-print Network

We calculate the pre-main-sequence HZ for stars of spectral classes F to M. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important in understanding how planets become habitable. Such worlds are interesting targets for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet to star separation for cool stars than is the case for the traditional main-sequence (MS) habitable zone (HZ). We use 1D radiative-convective climate and stellar evolutionary models to calculate pre-main-sequence HZ distances for F1 to M8 stellar types. We also show that accreting planets that are later located in the traditional MS HZ orbiting stars cooler than a K5 (including the full range of M-stars) receive stellar fluxes that exceed the ru...

Ramirez, Ramses M

2014-01-01

14

Determination of the habitable zone through planetary atmospheric absorption analysis  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

15

Relative stellar occurrence of exoplanets in habitable zones of the main sequence F, G, K stars  

NASA Astrophysics Data System (ADS)

We have determined the stellar occurrence of exoplanets in the habitable zones of the main sequence F, G, K stars using the statistical analysis of confirmed exoplanets and that of the Kepler candidates. We predict the greatest occurrence of exoplanets in the habitable zones of the main sequence G stars. An optimistic definition of habitable zone gives 0.114 Earth-size exoplanets per star in habitable zones of the main sequence G stars for the confirmed exoplanets and 0.336-0.041-0.032 Earth-size exoplanets per star in habitable zones of the main sequence G stars for the Kepler candidates. The possibility of detecting habitable exoplanets is much higher for the star from the main sequence G stars, the exoplanet detection missions can be focused in the region around the stars of this spectral class.

Pintr, Pavel; Pe?inová, Vlasta; Lukš, Antonín; Pathak, Anirban

2014-09-01

16

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

17

Habitable Zone Super-Earths with Non-Stabilised Spectrographs  

NASA Astrophysics Data System (ADS)

Detecting the small velocity amplitudes (<= 10 m/s) produced by habitable zone rocky planets around M Dwarfs requires radial velocity precisions of a few m s-1. However, an iodine absorption cell, commonly used as a high precision wavelength reference on non-stabilised spectrographs, is not efficient for very red and faint objects like M Dwarfs. Instead, arc lamps have to be used. With the exception of the ultra-stabilised HARPS spectrograph, achieving ~m s-1 calibration with arc lamps has not been possible because typical spectrographs experience drifts of several hundred m s-1 due to local atmospheric changes in pressure and temperature. We outline and present results from an innovative differential wavelength calibration method that enables ~m s-1 precision from non-stabilised, high-resolution spectrographs. This technique allows the detection of rocky planets with radial velocity amplitudes of a few m s-1.

Wright, Duncan J.; Tinney, Christopher G.; Wittenmyer, Robert A.

2014-04-01

18

The first Earth-sized habitable zone exoplanets  

NASA Astrophysics Data System (ADS)

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

Barclay, T.; Quintana, E.

2014-03-01

19

Planetary Atmosphere Stability in the Habitable Zones of M-stars  

Microsoft Academic Search

The traditional habitable zone depends on conditions suitable for long term stability of liquid water on the surface of planets. It is suggested that the frequent intense stellar CME events could have led to so rapid erosion of planetary atmospheres that generally speaking there is essentially no habitable zones around Earth-mass planets around M-stars. However, fast atmosperic mass loss should

Feng Tian

2010-01-01

20

TOWARD THE MINIMUM INNER EDGE DISTANCE OF THE HABITABLE ZONE  

E-print Network

We explore the minimum distance from a host star where an exoplanet could potentially be habitable in order not to discard close-in rocky exoplanets for follow-up observations. We find that the inner edge of the Habitable ...

Zsom, Andras

21

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

22

The habitable-zone planet finder calibration system  

NASA Astrophysics Data System (ADS)

We present the design concept of the wavelength calibration system for the Habitable-zone Planet Finder instrument (HPF), a precision radial velocity (RV) spectrograph designed to detect terrestrial-mass planets around M-dwarfs. HPF is a stabilized, fiber-fed, R~50,000 spectrograph operating in the near-infrared (NIR) z/Y/J bands from 0.84 to 1.3 microns. For HPF to achieve 1 m s-1 or better measurement precision, a unique calibration system, stable to several times better precision, will be needed to accurately remove instrumental effects at an unprecedented level in the NIR. The primary wavelength calibration source is a laser frequency comb (LFC), currently in development at NIST Boulder, discussed separately in these proceedings. The LFC will be supplemented by a stabilized single-mode fiber Fabry-Perot interferometer reference source and Uranium-Neon lamp. The HPF calibration system will combine several other new technologies developed by the Penn State Optical-Infrared instrumentation group to improve RV measurement precision including a dynamic optical coupling system that significantly reduces modal noise effects. Each component has been thoroughly tested in the laboratory and has demonstrated significant performance gains over previous NIR calibration systems.

Halverson, Samuel; Mahadevan, Suvrath; Ramsey, Lawrence; Terrien, Ryan; Roy, Arpita; Schwab, Christian; Bender, Chad; Hearty, Fred; Levi, Eric; Osterman, Steve; Ycas, Gabe; Diddams, Scott

2014-08-01

23

Kepler Mission: Detecting Earth-sized Planets in Habitable Zones  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

24

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

25

Habitable Evaporated Cores: Converting Mini-Neptunes into Super- Earths in the Habitable Zone of M Dwarfs  

NASA Astrophysics Data System (ADS)

The low masses and luminosities of M dwarfs make them ideal targets for thedetection of terrestrial planets in the habitable zone (HZ). However, studies suggest that planets formed only from material in the HZs of these stars are likely to be small and dry (e.g., Raymond et al. 2007). As a result, many of the planets that will be detected in the HZ by upcoming missions are probably the result of migration from beyond the snow line, and may have formed with large H/He envelopes (so-called mini-Neptunes). Here we show that photoevaporation and Roche lobe overflow of these planets can lead to the complete loss of their gaseous envelopes, transforming them into potentially habitable worlds, which we call “habitable evaporated cores”. We couple the planet structure models of Lopez et al. (2012) with a simple Roche lobe overflow scheme and the X-ray/extreme ultraviolet (XUV)-induced mass loss model of Erkaev et al. (2007). We also couple the orbital effects of anisotropic mass loss with tidal evolution and show that this coupling can lead to orbital changes that significantly enhance the mass loss rate.Habitable evaporated cores are most likely to form from small mini-Neptunes (?4 M?) with large (?50%) initial hydrogen fractions orbiting M4 stars and later. Given the steep decrease in stellar XUV flux with time (Ribas et al. 2005), mass loss is negligible after ~1 Gyr, at which point a habitable evaporated core is capable of degassing and maintaining a secondary atmosphere. This process may be the dominant formation mechanism for habitable planets around M dwarfs, and may be discovered by missions such as TESS and PLATO.

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

2014-03-01

26

Habitable evaporated cores: transforming mini-neptunes into super-earths in the habitable zones of m dwarfs.  

PubMed

We show that photoevaporation of small gaseous exoplanets ("mini-Neptunes") in the habitable zones of M dwarfs can remove several Earth masses of hydrogen and helium from these planets and transform them into potentially habitable worlds. We couple X-ray/extreme ultraviolet (XUV)-driven escape, thermal evolution, tidal evolution, and orbital migration to explore the types of systems that may harbor such "habitable evaporated cores" (HECs). We find that HECs are most likely to form from planets with ?1 M? solid cores with up to about 50% H/He by mass, though whether or not a given mini-Neptune forms a HEC is highly dependent on the early XUV evolution of the host star. As terrestrial planet formation around M dwarfs by accumulation of local material is likely to form planets that are small and dry, evaporation of small migrating mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich Earths around these stars. Key Words: Astrobiology-Extrasolar terrestrial planets-Habitability-Planetary atmospheres-Tides. Astrobiology 15, 57-88. PMID:25590532

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

2015-01-01

27

Constraining the Radiation and Plasma Environment of the Kepler Circumbinary Habitable Zone Planets  

E-print Network

The remarkable discovery of many planets and candidates using the Kepler telescope even includes ten planets orbiting eight binaries. Three out of the eight, Kepler 16, Kepler 47, and KIC 9632895, have at least one planet in the circumbinary habitable zone (BHZ). In previous work (Mason et al. 2013), we investigated the potential habitability of Earth-like circumbinary planets. In particular, we highlighted the role of mutual stellar tidal interaction and the resulting impact on terrestrial planet habitability. The Kepler binaries with planets in the BHZ are studied in order to constrain the high energy radiation and plasma environment of potentially habitable circumbinary planets. The limits of the BHZ in these binaries as a function of time are estimated and the habitability lifetime is calculated. A self-consistent model of the evolution of stellar rotation including the effect of tidal interaction is key to establishing the plasma and radiation environment. A comprehensive model of the evolution of stella...

Zuluaga, Jorge I; Cuartas, Pablo A

2015-01-01

28

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

29

Can Life develop in the expanded habitable zones around Red Giant Stars?  

E-print Network

We present some new ideas about the possibility of life developing around sub-giant and red giant stars. Our study concerns the temporal evolution of the habitable zone. The distance between the star and the habitable zone, as well as its width, increases with time as a consequence of stellar evolution. The habitable zone moves outward after the star leaves the main sequence, sweeping a wider range of distances from the star until the star reaches the tip of the asymptotic giant branch. If life could form and evolve over time intervals from $5 \\times 10^8$ to $10^9$ years, then there could be habitable planets with life around red giant stars. For a 1 M$_{\\odot}$ star at the first stages of its post main-sequence evolution, the temporal transit of the habitable zone is estimated to be of several 10$^9$ years at 2 AU and around 10$^8$ years at 9 AU. Under these circumstances life could develop at distances in the range 2-9 AU in the environment of sub-giant or giant stars and in the far distant future in the environment of our own Solar System. After a star completes its first ascent along the Red Giant Branch and the He flash takes place, there is an additional stable period of quiescent He core burning during which there is another opportunity for life to develop. For a 1 M$_{\\odot}$ star there is an additional $10^9$ years with a stable habitable zone in the region from 7 to 22 AU. Space astronomy missions, such as proposed for the Terrestrial Planet Finder (TPF) and Darwin should also consider the environments of sub-giants and red giant stars as potentially interesting sites for understanding the development of life.

Bruno Lopez; Jean Schneider; William C. Danchi

2005-03-23

30

Stability of Earth-Mass Planets in the Habitable Zones of Extrasolar Planetary Systems  

E-print Network

Stability of Earth-Mass Planets in the Habitable Zones of Extrasolar Planetary Systems Dr. Ravi Kumar Kopparapu Dept. of Geosciences, College of Earth and Mineral Science Over 500 planets orbiting and Saturn but in the last couple of years several "super-earths", planets with mass less than 10 times Earth

Bjørnstad, Ottar Nordal

31

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

SciTech Connect

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

Gong Yanxiang; Zhou Jilin; Xie Jiwei, E-mail: yxgong@nju.edu.cn, E-mail: zhoujl@nju.edu.cn [Department of Astronomy and Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093 (China)

2013-01-20

32

Asynchronous rotation of Earth-like planets in the habitable zone of lower-mass stars  

E-print Network

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

Leconte, Jérémy; Menou, Kristen; Murray, Norman

2015-01-01

33

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

E-print Network

The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The interferometric study presented here yields directly determined values for 55 Cnc's stellar astrophyiscal parameters: $R=0.943 \\pm 0.010 R_{\\odot}$, $T_{\\rm EFF} = 5196 \\pm 24$ K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 $\\pm$ 2.5 Gyr, implying a stellar mass of $0.905 \\pm 0.015 M_{\\odot}$. Our analysis of the location and extent of the system's habitable zone (0.67--1.32 AU) shows that planet f ($M \\sin i = 0.155 M_{Jupiter}$) spends the majority of the duration of its elliptical orbit in the circumstellar habitable zone, where, with moderate greenhouse heating, it could harbor liquid water. 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 ($\\sim 2.05 \\pm 0.15 R_{\\earth}$), which, depending on the planetary mass assumed, implies a bulk density of 0.76 $\\rho_{\\earth}$ or 1.07 $\\rh...

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

2011-01-01

34

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

35

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

36

Exomoon Habitability Constrained by Illumination and Tidal Heating  

PubMed Central

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

2013-01-01

37

MOA-2011-BLG-293Lb: First Microlensing Planet Possibly in the Habitable Zone  

NASA Astrophysics Data System (ADS)

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

Batista, V.; Beaulieu, J.-P.; Gould, A.; Bennett, D. P.; Yee, J. C.; Fukui, A.; Gaudi, B. S.; Sumi, T.; Udalski, A.

2014-01-01

38

The galactic habitable zone of the Milky Way and M31 from chemical evolution models with gas radial flows  

NASA Astrophysics Data System (ADS)

The galactic habitable zone is defined as the region with sufficient abundance of heavy elements to form planetary systems in which Earth-like planets could be born and might be capable of sustaining life, after surviving to close supernova explosion events. Galactic chemical evolution models can be useful for studying the galactic habitable zones in different systems. We apply detailed chemical evolution models including radial gas flows to study the galactic habitable zones in our Galaxy and M31. We compare the results to the relative galactic habitable zones found with `classical' (independent ring) models, where no gas inflows were included. For both the Milky Way and Andromeda, the main effect of the gas radial inflows is to enhance the number of stars hosting a habitable planet with respect to the `classical' model results, in the region of maximum probability for this occurrence, relative to the classical model results. These results are obtained by taking into account the supernova destruction processes. In particular, we find that in the Milky Way the maximum number of stars hosting habitable planets is at 8 kpc from the Galactic Centre, and the model with radial flows predicts a number which is 38 per cent larger than what was predicted by the classical model. For Andromeda we find that the maximum number of stars with habitable planets is at 16 kpc from the centre and that in the case of radial flows this number is larger by 10 per cent relative to the stars predicted by the classical model.

Spitoni, E.; Matteucci, F.; Sozzetti, A.

2014-05-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

40

The Properties of Exomoons Around the Habitable Zone Planet, Kepler 22b  

NASA Astrophysics Data System (ADS)

As part of a larger study to understand the formation, evolution, and stability of satellites around exoplanets, we have examined the Kepler 22 system. A single planet of mass 2 × 1026 kg, Kepler 22b orbits within the habitable zone (Kopparapu et al. 2013) at 0.85 AU. While Kepler 22b may be habitable, there also exists the possibility that any satellites of the planet may also be life sustaining.A series of N-body simulations were performed to examine the most probable configuration of moons orbiting Kepler 22b. Initially, a moonlet disk of 100 bodies (mdisk = 4.29 × 1022 kg) was randomly placed around Kepler 22b. The moonlet disk spanned 10 - 80% of Kepler 22b's Hill sphere (Kasting et al. 1993). Simulations were run for 500 kyrs, with the star, planet, and moonlets allowed to gravitationally evolve.The Kepler 22b system was able to retain three to four moons in 96% of the simulations. . The remaining simulations produced systems of two moons on highly eccentric orbits. It is unlikely that the two-moon configuration would remain stable for a significant amount of time. We present the properties of the stable satellites. We have run an additional set of simulations examining the rotational effects satellites will have on Kepler 22b, given the high likelihood that the planet possesses a system of moons. We were specifically investigating if the presence of moons reduces the precession of Kepler 22b, increasing the planet's habitability.

Fuse, Christopher R.; Bokorney, Jake

2015-01-01

41

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

42

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

43

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

44

Direct imaging of exoplanets in the habitable zone with adaptive optics  

NASA Astrophysics Data System (ADS)

One of the primary goals of exoplanet science is to find and characterize habitable planets, and direct imaging will play a key role in this effort. Though imaging a true Earth analog is likely out of reach from the ground, the coming generation of giant telescopes will find and characterize many planets in and near the habitable zones (HZs) of nearby stars. Radial velocity and transit searches indicate that such planets are common, but imaging them will require achieving extreme contrasts at very small angular separations, posing many challenges for adaptive optics (AO) system design. Giant planets in the HZ may even be within reach with the latest generation of high-contrast imagers for a handful of very nearby stars. Here we will review the definition of the HZ, and the characteristics of detectable planets there. We then review some of the ways that direct imaging in the HZ will be different from the typical exoplanet imaging survey today. Finally, we present preliminary results from our observations of the HZ of ? Centauri A with the Magellan AO system's VisAO and Clio2 cameras.

Males, Jared R.; Close, Laird M.; Guyon, Olivier; Morzinski, Katie; Puglisi, Alfio; Hinz, Philip; Follette, Katherine B.; Monnier, John D.; Tolls, Volker; Rodigas, Timothy J.; Weinberger, Alycia; Boss, Alan; Kopon, Derek; Wu, Ya-lin; Esposito, Simone; Riccardi, Armando; Xompero, Marco; Briguglio, Runa; Pinna, Enrico

2014-07-01

45

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

46

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

48

An Earth-sized Planet in the Habitable Zone of a Cool Star  

E-print Network

The quest for Earth-like planets represents a major focus of current exoplanet research. While planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surface. We present the detection of Kepler-186f, a 1.11+\\-0.14 Earth radius planet that is the outermost of five planets - all roughly Earth-sized - that transit a 0.47+\\-0.05 Rsun star. The intensity and spectrum of the star's radiation places Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and H2O at its surface, then some of this H2O is likely to be in liquid form.

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

2014-01-01

49

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

SciTech Connect

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 [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States); Kaltenegger, Lisa [MPIA, Koenigstuhl 17, Heidelberg, D-69117 (Germany)

2013-11-10

50

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

51

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

2013-01-01

52

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

SciTech Connect

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

Morales, Farisa Y.; Bryden, G.; Werner, M. W. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Padgett, D. L. [Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Furlan, E., E-mail: Farisa@jpl.nasa.gov [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)

2012-09-20

53

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

PubMed

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

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

2015-02-01

54

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

SciTech Connect

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 [MPIA, Koenigstuhl 17, D-69117 Heidelberg (Germany); Haghighipour, Nader, E-mail: kaltenegger@mpia.de [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States)

2013-11-10

55

Habitable Zones around Main-sequence Stars: Dependence on Planetary Mass  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

56

Space mission and instrument design to image the Habitable Zone of Alpha Centauri  

NASA Astrophysics Data System (ADS)

The Alpha Centauri System is particularly well suited for high-contrast imaging. The angular separation of the A and B stars Habitable Zone ranges from 0.7' to 1.63' and 0.4' to 0.95' respectively, with contrast ratios for an earth-like planet in the order of 10-10. A 35cm telescope using an aggressive coronagraph is capable of imaging and constrain the contents of earth-like, or larger planets, from the inner HZ out to the equivalent orbit of a Jupiter class planet. Here we present a mission concept design, which considers an off-axis telescope with elliptical aperture primary mirror, an embedded Phase Induced Amplitude Apodization lossless Coronagraph (PIAA), and a Kilo DM deformable mirror for wavefront control and speckle nulling. Our goal is to obtain 2x1011contrast at 0.7' and 6x1011contrast at 0.4' after post processing. To solve the binary diffraction contamination we will use the Multiple Star Wavefront Control approach than can correct for the light of both stars. We baseline a 3 year mission on a heliocentric orbit, that provides a thermally stable environment and continuous access to the target.

Bendek, Eduardo; Belikov, Ruslan; Thomas, Sandrine; Lozi, Julien

2015-01-01

57

Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

58

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

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

59

Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone  

E-print Network

We present an investigation of twelve candidate transiting planets from Kepler with orbital periods ranging from 34 to 207 days, selected from initial indications that they are small and potentially in the habitable zone (HZ) of their parent stars. The expected Doppler signals are too small to confirm them by demonstrating that their masses are in the planetary regime. Here we verify their planetary nature by validating them statistically using the BLENDER technique, which simulates large numbers of false positives and compares the resulting light curves with the Kepler photometry. This analysis was supplemented with new follow-up observations (high-resolution optical and near-infrared spectroscopy, adaptive optics imaging, and speckle interferometry), as well as an analysis of the flux centroids. For eleven of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01, 3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the likelihood they are true planets is far greater than that of a false po...

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

2015-01-01

60

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

61

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

SciTech Connect

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

Kipping, D. M. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Forgan, D. [Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Hartman, J.; Bakos, G. Á. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 05844 (United States); Nesvorný, D. [Department of Space Studies, Southwest Research Institute, Boulder, CO 80302 (United States); Schmitt, A.; Buchhave, L., E-mail: dkipping@cfa.harvard.edu [Niels Bohr Institute, Copenhagen University (Denmark)

2013-11-10

62

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

63

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

SciTech Connect

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

Barclay, Thomas; Burke, Christopher J.; Howell, Steve B.; Rowe, Jason F.; Huber, Daniel; Jenkins, Jon M.; Quintana, Elisa V.; Still, Martin; Twicken, Joseph D.; Bryson, Stephen T.; Borucki, William J.; Caldwell, Douglas A.; Clarke, Bruce D.; Christiansen, Jessie L; Coughlin, Jeffrey L. [NASA Ames Research Center, M/S 244-30, Moffett Field, CA 94035 (United States); Isaacson, Howard; Kolbl, Rea; Marcy, Geoffrey W. [Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720 (United States); Ciardi, David [NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Fischer, Debra A. [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); and others

2013-05-10

64

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

PubMed Central

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

Adande, Gilles R.; Woolf, Neville J.

2013-01-01

65

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

2013-05-01

66

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

67

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

68

On the influence of the Kozai mechanism in habitable zones of extrasolar planetary systems  

NASA Astrophysics Data System (ADS)

Aims: We investigate the long-term evolution of inclined test particles representing a small Earth-like body with negligible gravitational effects (hereafter called massless test-planets) in the restricted three-body problem, and consisting of a star, a gas giant, and a massless test-planet. The test-planet is initially on a circular orbit and moves around the star at distances closer than the gas giant. The aim is to show the influences of the eccentricity and the mass of the gas giant on the dynamics, for various inclinations of the test-planet, and to investigate in more detail the Kozai mechanism in the elliptic problem. Methods: We performed a parametric study, integrating the orbital evolution of test particles whose initial conditions were distributed on the semi-major axis - inclination plane. The gas giant's initial eccentricity was varied. For the calculations, we used the Lie integration method and in some cases the Bulirsch-Stoer algorithm. To analyze the results, the maximum eccentricity and the Lyapunov characteristic indicator were used. All integrations were performed for 105 periods of the gas giant. Results: Our calculations show that inclined massless test-planets can be in stable configurations with gas giants on either circular or elliptic orbits. The higher the eccentricity of the gas giant, the smaller the possible range in semi-major axis for the test-planet. For gas giants on circular orbits, our results illustrate the well-known results associated with the Kozai mechanism, which do not allow stable orbits above a critical inclination of approximately 40°. For gas giants on eccentric orbits, the dynamics is quite similar, and the massless companion exhibits limited variations in eccentricity. In addition, we identify a region around 35° consisting of long-time stable, low eccentric orbits. We show that these results are also valid for Earth-mass companions, therefore they can be applied to extrasolar systems: for instance, the extrasolar planetary system HD 154345 can possess a 35° degree inclined, nearly circular, Earth-mass companion in the habitable zone.

Funk, B.; Libert, A.-S.; Süli, Á.; Pilat-Lohinger, E.

2011-02-01

69

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

SciTech Connect

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

Danchi, William C. [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States); Lopez, Bruno, E-mail: william.c.danchi@nasa.gov, E-mail: bruno.lopez@oca.eu [Observatoire de la Cote d'Azur, Laboratoire Lagrange UMR 7293, BP 4229, F-06034 Nice Cedex 4 (France)

2013-05-20

70

Extreme water loss and abiotic o2 buildup on planets throughout the habitable zones of m dwarfs.  

PubMed

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

Luger, R; Barnes, R

2015-02-01

71

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

72

Extreme Water Loss and Abiotic O2 Buildup On Planets Throughout the Habitable Zones of M Dwarfs  

NASA Astrophysics Data System (ADS)

We show that terrestrial planets in the habitable zones of M dwarfs older than ~1 Gyr could have been in runaway greenhouses for several hundred Myr following their formation due to the star's extended pre-main sequence phase. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone. We find that the amount of water lost roughly scales with the planet mass: super-Earths, which lose water primarily via the escape of hydrogen, lose more water than Earth-mass planets, which lose water more slowly via the escape of both hydrogen and oxygen. If the surface is able to absorb most of the photolytically produced oxygen, planets around low mass M dwarfs can be completely desiccated for initial inventories of up to several tens of Earth oceans. On the other hand, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bars of abiotically produced O2, resulting in potential false positives for life. The amount of O2 that builds up also scales with the planet mass; we find that O2 builds up at a constant rate of ~5 bars/Myr on Earth-mass planets and up to ~25 bars/Myr on super- Earths. The fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. In general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low mass stars.

Luger, Rodrigo; Barnes, Rory

2015-01-01

73

Formation, Habitability, and Detection of Extrasolar Moons  

E-print Network

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

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

2014-01-01

74

The EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE)  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

75

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

76

The habitable-zone planet finder: a stabilized fiber-fed NIR spectrograph for the Hobby-Eberly Telescope  

NASA Astrophysics Data System (ADS)

We present the scientific motivation and conceptual design for the recently funded Habitable-zone Planet Finder (HPF), a stabilized fiber-fed near-infrared (NIR) spectrograph for the 10 meter class Hobby-Eberly Telescope (HET) that will be capable of discovering low mass planets around M dwarfs. The HPF will cover the NIR Y and J bands to enable precise radial velocities to be obtained on mid M dwarfs, and enable the detection of low mass planets around these stars. The conceptual design is comprised of a cryostat cooled to 200K, a dual fiber-feed with a science and calibration fiber, a gold coated mosaic echelle grating, and a Teledyne Hawaii-2RG (H2RG) *NIR detector with a 1.7?m cutoff. A uranium-neon hollow-cathode lamp is the baseline wavelength calibration source, and we are actively testing laser frequency combs to enable even higher radial velocity precision. We will present the overall instrument system design and integration with the HET, and discuss major system challenges, key choices, and ongoing research and development projects to mitigate risk. We also discuss the ongoing process of target selection for the HPF survey.

Mahadevan, Suvrath; Ramsey, Lawrence; Bender, Chad; Terrien, Ryan; Wright, Jason T.; Halverson, Sam; Hearty, Fred; Nelson, Matt; Burton, Adam; Redman, Stephen; Osterman, Steven; Diddams, Scott; Kasting, James; Endl, Michael; Deshpande, Rohit

2012-09-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

78

Root foraging and yield components underlying limited effects of Partial Root-zone Drying on oilseed rape, a crop with an indeterminate growth habit  

Microsoft Academic Search

We report on two experiments with oilseed rape (Brassica napus L.) to test if partial root-zone drying techniques improve yield in a crop in which vegetative and reproductive growth overlap\\u000a (indeterminate growth habit), and to investigate what plant morphological responses contribute to the yield that is realized.\\u000a Deficit irrigation resulted in smaller plants with smaller yields but larger seeds compared

Jingfeng Wang; Hans de Kroon; Ling Wang; Hannie de Caluwe; Gerard M. Bögemann; Gerard M. van der Weerden; Shaozhong Kang; Antoine J. M. Smits

2009-01-01

79

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

E-print Network

We report the latest Planet Hunter results, including PH2 b, a Jupiter-size (R_PL = 10.12 \\pm 0.56 R_E) 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 three 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 Neptune to Jupiter. These detections nearly double the number of gas giant planet candidates orbiting at habitable zone distances. We conducted spectroscopic observat...

Wang, Ji; 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; Giguere, Matthew J; Brewer, John M; Lynn, Stuart; Simpson, Robert; Hoekstra, Abe J; Jacobs, Thomas Lee; LaCourse, Daryll; Schwengeler, Hans Martin; Chopin, Mike

2013-01-01

80

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

81

The evolution of habitable zones during stellar lifetimes and its implications on the search for extraterrestrial life  

E-print Network

A stellar evolution computer model has been used to determine changes in the luminosity L and effective temperature T(e) of single stars during their time on the main sequence. The range of stellar masses investigated was from 0.5 to 1.5 times that of the Sun, each with a mass fraction of metals (metallicity, Z) from 0.008 to 0.05. The extent of each star's habitable zone (HZ) has been determined from its values of L and T(e). These stars form a reference framework for other main sequence stars. All of the 104 main sequence stars known to have one or more giant planets have been matched to their nearest stellar counterpart in the framework, in terms of mass and metallicity, hence closely approximating their HZ limits. The limits of HZ, for each of these stars, have been compared to its giant planet(s)'s range of strong gravitational influence. This allows a quick assessment as to whether Earth-mass planets could exist in stable orbits within the HZ of such systems, both presently and at any time during the star's main sequence lifetime. A determination can also be made as to the possible existence of life-bearing satellites of giant planets, which orbit within HZs. Results show that about half of the 104 known extrasolar planetary systems could possibly have been housing an Earth-mass planet in HZs during at least the past billion years, and about three-quarters of the 104 could do so for at least a billion years at some time during their main sequence lives. Whether such Earth-mass planets could have formed is an urgent question now being investigated by others, with encouraging results.

David R. Underwood; Barrie W. Jones; P. Nick Sleep

2003-12-19

82

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

SciTech Connect

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

Wang, Ji; Fischer, Debra A.; Boyajian, Tabetha S.; Schmitt, Joseph R.; Giguere, Matthew J.; Brewer, John M. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Barclay, Thomas [NASA Ames Research Center, M/S 244-30, Moffett Field, CA 94035 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Schwamb, Megan E. [Department of Physics, Yale University, P.O. Box 208121, New Haven, CT 06520 (United States); Lintott, Chris; Simpson, Robert [Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Jek, Kian J.; Hoekstra, Abe J.; Jacobs, Thomas Lee; LaCourse, Daryll; Schwengeler, Hans Martin; Smith, Arfon M.; Parrish, Michael; Lynn, Stuart [Adler Planetarium, 1300 South Lake Shore Drive, Chicago, IL 60605 (United States); Schawinski, Kevin, E-mail: ji.wang@yale.edu [Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 16, CH-8093 Zurich (Switzerland); and others

2013-10-10

83

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

84

Formation, Habitability, and Detection of Extrasolar Moons  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

85

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

NASA Astrophysics Data System (ADS)

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

Cuntz, Manfred

2015-01-01

86

Embryos grown in the dead zone: Assembling the first protoplanetary cores in low mass self-gravitating circumstellar disks of gas and solids  

E-print Network

In the borders of the dead zones of protoplanetary disks, the inflow of gas produces a local density maximum that triggers the Rossby wave instability. The vortices that form are efficient in trapping solids. We aim to assess the possibility of gravitational collapse of the solids within the Rossby vortices. We perform global simulations of the dynamics of gas and solids in a low mass non-magnetized self-gravitating thin protoplanetary disk with the Pencil code. We use multiple particle species of radius 1, 10, 30, and 100 cm. The dead zone is modeled as a region of low viscosity. The Rossby vortices excited in the edges of the dead zone are very efficient particle traps. Within 5 orbits after their appearance, the solids achieve critical density and undergo gravitational collapse into Mars sized objects. The velocity dispersions are of the order of 10 m/s for newly formed embryos, later lowering to less than 1 m/s by drag force cooling. After 200 orbits, 38 gravitationally bound embryos were formed inside the vortices, half of them being more massive than Mars. The embryos are composed primarily of same-sized particles. We conclude that the presence of a dead zone naturally gives rise to a population of protoplanetary cores in the mass range of 0.1-0.6 Earth masses, on very short timescales.

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

2008-10-14

87

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

SciTech Connect

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

Haghighipour, Nader [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States); Vogt, Steven S.; Rivera, Eugenio J.; Laughlin, Greg; Meschiari, Stefano [Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Paul Butler, R. [Department of Terrestrial Magnetism, Carnegie Institute of Washington, Washington, DC 20015 (United States); Henry, Gregory W. [Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37209 (United States)

2010-05-20

88

Habitable Trinity  

NASA Astrophysics Data System (ADS)

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

Dohm, J. M.; Maruyama, S.

2013-12-01

89

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

90

Origin and loss of nebula-captured hydrogen envelopes from `sub'- to `super-Earths' in the habitable zone of Sun-like stars  

NASA Astrophysics Data System (ADS)

We investigate the origin and loss of captured hydrogen envelopes from protoplanets having masses in a range between `sub-Earth'-like bodies of 0.1 M? and `super-Earths' with 5 M? in the habitable zone at 1 au of a Sun-like G star, assuming that their rocky cores had formed before the nebula gas dissipated. We model the gravitational attraction and accumulation of nebula gas around a planet's core as a function of protoplanetary luminosity during accretion and calculate the resulting surface temperature by solving the hydrostatic structure equations for the protoplanetary nebula. Depending on nebular properties, such as the dust grain depletion factor, planetesimal accretion rates, and resulting luminosities, for planetary bodies of 0.1-1 M? we obtain hydrogen envelopes with masses between ˜2.5 × 1019 and 1.5 × 1026 g. For `super-Earths' with masses between 2 and 5 M? more massive hydrogen envelopes within the mass range of ˜7.5 × 1023-1.5 × 1028 g can be captured from the nebula. For studying the escape of these accumulated hydrogen-dominated protoatmospheres, we apply a hydrodynamic upper atmosphere model and calculate the loss rates due to the heating by the high soft-X-ray and extreme ultraviolet (XUV) flux of the young Sun/star. The results of our study indicate that under most nebula conditions `sub-Earth' and Earth-mass planets can lose their captured hydrogen envelopes by thermal escape during the first ˜100 Myr after the disc dissipated. However, if a nebula has a low dust depletion factor or low accretion rates resulting in low protoplanetary luminosities, it is possible that even protoplanets with Earth-mass cores may keep their hydrogen envelopes during their whole lifetime. In contrast to lower mass protoplanets, more massive `super-Earths', which can accumulate a huge amount of nebula gas, lose only tiny fractions of their primordial hydrogen envelopes. Our results agree with the fact that Venus, Earth, and Mars are not surrounded by dense hydrogen envelopes, as well as with the recent discoveries of low density `super-Earths' that most likely could not get rid of their dense protoatmospheres.

Lammer, H.; Stökl, A.; Erkaev, N. V.; Dorfi, E. A.; Odert, P.; Güdel, M.; Kulikov, Yu. N.; Kislyakova, K. G.; Leitzinger, M.

2014-04-01

91

Habitable exoplanets statistics in the Milky Way  

NASA Astrophysics Data System (ADS)

We present an exoplanet statistical analysis into the Milky Way. We use the Becanson galactic synthetic model to simulate the Milky Way and the galactic and stellar habitable zones to calculate habitable planets. To assess habitability on the Galactic scale, we model supernova rates and planet formation. Our study, models the SNII and SNIa sterilizations by selecting them from within this preexisting stellar population. Furthermore, we consider habitability on tidally locked and non-tidally locked planets separately, and study habitability as a function of height above and below the Galactic mid-plane. The number of total habitable planets makes Milky Way practically empty of habitable planets. Our results, from these simulations, agree very well with Kepler's discoveries. Finally, we apply our results to the PLATO future space mission.

Anagnos, Th.

2013-09-01

92

Exoplanet habitability.  

PubMed

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

Seager, Sara

2013-05-01

93

Tides and the Evolution of Planetary Habitability  

E-print Network

Tides raised on a planet by its host star's gravity can reduce a 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 (<0.35 M_Sun). Such migration may have important implications for the evolution of the atmosphere, internal heating and the Gaia hypothesis. Similarly, a planet detected interior to the habitable zone could have been habitable in the past. We consider the past habitability of the recently-discovered, ~5 M_Earth 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 we include constraints derived from the additional companions, we see that most parameter choices that predict 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.

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

2008-07-04

94

The Copernicus observations - Interstellar or circumstellar material. [UV spectra of early stars  

NASA Technical Reports Server (NTRS)

It is suggested that the sharp absorption lines observed in the ultraviolet spectra of early-type stars by the Copernicus satellite may be entirely accounted for by the circumstellar material in the H II regions and associated transition zones around the observed stars. If this interpretation is correct, the Copernicus results yield little information on the state of any interstellar (as opposed to circumstellar) gas and, in particular, shed little light on the degree of element depletion in interstellar space.

Steigman, G.; Strittmatter, P. A.; Williams, R. E.

1975-01-01

95

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

96

The structure of circumstellar shells  

NASA Technical Reports Server (NTRS)

Speckle-interferometric measurements are reported for the brightness distributions of the OH/IR stars OH 26.5 + 0.6 and IRC + 10420 at wavelengths which are near the center of and just outside the 10-micron absorption/emission feature produced by circumstellar dust. For OH 26.5 + 0.6, the angular size within the absorption feature is 0.50 + or - 0.02 arcsec, while the angular size outside the feature is less than 0.2 arcsec. For IRC + 10420, the angular sizes inside and outside the emission feature are both 0.42 + or - 0.02 arcsec. Simple models of the circumstellar shells are calculated which can account for the measured angular sizes and flux distributions of the objects. The models give the wavelength dependence of the opacity of the circumstellar material, which is quite different for the two objects.

Fix, John D.; Cobb, Michael L.

1988-01-01

97

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

98

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

99

Study HabitsStudy Habits Homework strategies  

E-print Network

Study HabitsStudy Habits Homework strategies #12;Course structureCourse structure · In here you have homeworks that tend to relyIn here you have homeworks that tend to rely on handwritten work · You thoughts · Treat your homeworks & projects as you ld l twould lecture ­ They are part of the course

Wolverton, Steve

100

The Habitable-zone Planet Finder: A status update on the development of a stabilized fiber-fed near-infrared spectrograph for the for the Hobby-Eberly telescope  

NASA Astrophysics Data System (ADS)

The Habitable-Zone Planet Finder is a stabilized, fiber-fed, NIR spectrograph being built for the 10m Hobby- Eberly telescope (HET) that will be capable of discovering low mass planets around M dwarfs. The optical design of the HPF is a white pupil spectrograph layout in a vacuum cryostat cooled to 180 K. The spectrograph uses gold-coated mirrors, a mosaic echelle grating, and a single Teledyne Hawaii-2RG (H2RG) NIR detector with a 1.7-micron cutoff covering parts of the information rich z, Y and J NIR bands at a spectral resolution of R˜50,000. The unique design of the HET requires attention to both near and far-field fiber scrambling, which we accomplish with double scramblers and octagonal fibers. In this paper we discuss and summarize the main requirements and challenges of precision RV measurements in the NIR with HPF and how we are overcoming these issues with technology, hardware and algorithm developments to achieve high RV precision and address stellar activity.

Mahadevan, Suvrath; Ramsey, Lawrence W.; Terrien, Ryan; Halverson, Samuel; Roy, Arpita; Hearty, Fred; Levi, Eric; Stefansson, Gudmundur K.; Robertson, Paul; Bender, Chad; Schwab, Chris; Nelson, Matt

2014-07-01

101

The HARPS search for southern extrasolar planets: XXXVI. New multi-planet systems in the HARPS volume limited sample: a super-Earth and a Neptune in the habitable zone  

E-print Network

The vast diversity of planetary systems detected to date is defying our capability of understanding their formation and evolution. Well-defined volume-limited surveys are the best tool at our disposal to tackle the problem, via the acquisition of robust statistics of the orbital elements. We are using the HARPS spectrograph to conduct our survey of ~850 nearby solar-type stars, and in the course of the past nine years we have monitored the radial velocity of HD103774, HD109271, and BD-061339. In this work we present the detection of five planets orbiting these stars, with m*sin(i) between 0.6 and 7 Neptune masses, four of which are in two multiple systems, comprising one super-Earth and one planet within the habitable zone of a late-type dwarf. Although for strategic reasons we chose efficiency over precision in this survey, we have the capability to detect planets down to the Neptune and super-Earth mass range, as well as multiple systems, provided that enough data points are made available.

Curto, G Lo; Benz, W; Bouchy, F; Hebrard, G; Lovis, C; Moutou, C; Naef, D; Pepe, F; Queloz, D; Santos, N C; Segransan, D; Udry, S

2013-01-01

102

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

2010-01-01

103

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

104

The HARPS search for southern extra-solar planets . XXXII. New multi-planet systems in the HARPS volume limited sample: a super-Earth and a Neptune in the habitable zone  

NASA Astrophysics Data System (ADS)

The vast diversity of planetary systems detected to date is defying our capability of understanding their formation and evolution. Well-defined volume-limited surveys are the best tool at our disposal to tackle the problem, via the acquisition of robust statistics of the orbital elements. We are using the HARPS spectrograph to conduct our survey of ?850 nearby solar-type stars, and in the course of the past nine years we have monitored the radial velocity of HD 103774, HD 109271, and BD-061339. In this work we present the detection of five planets orbiting these stars, with msin (i) between 0.6 and 7 Neptune masses, four of which are in two multiple systems, comprising one super-Earth and one planet within the habitable zone of a late-type dwarf. Although for strategic reasons we chose efficiency over precision in this survey, we have the capability to detect planets down to the Neptune and super-Earth mass range as well as multiple systems, provided that enough data points are made available. Based on observations made with the HARPS instrument on the ESO 3.6 m telescope at La Silla (Chile), under the GTO program ID 072.C-0488 and the regular programs: 085.C-0019, 087.C-0831 and 089.C-0732. RV data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A59

Lo Curto, G.; Mayor, M.; Benz, W.; Bouchy, F.; Hébrard, G.; Lovis, C.; Moutou, C.; Naef, D.; Pepe, F.; Queloz, D.; Santos, N. C.; Segransan, D.; Udry, S.

2013-03-01

105

On the Habitability of Aquaplanets  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

106

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

107

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

2010-01-01

108

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

SciTech Connect

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

Liu Huigen; Zhang Hui; Zhou Jilin, E-mail: huigen@nju.edu.cn [School of Astronomy and Space Science and Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093 (China)

2013-04-20

109

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

110

Habitability study shuttle orbiter  

NASA Technical Reports Server (NTRS)

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

1973-01-01

111

Defining and measuring habit  

E-print Network

Habits are behavioral tendencies to repeat a well-learned response in a stable context with only minimal or sporadic cognitive monitoring. With repeated performance in a given context, the actor develops a cognitive association between contextual...

Quinn, Jeffrey M.

2001-01-01

112

Habitability design for spacecraft  

NASA Technical Reports Server (NTRS)

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

Franklin, G. C.

1978-01-01

113

Habitability: CAMELOT 4  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

114

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 ...

115

Changing your sleep habits  

MedlinePLUS

... these patterns over many years, they become habits. Insomnia is difficulty falling asleep or staying asleep. In many cases, you can relieve insomnia by making a few simple lifestyle changes. However, ...

116

Circumstellar gas in beta Pic  

NASA Astrophysics Data System (ADS)

From the very early observations completed in 1984, it was clear that some gas was present in the circumstellar environment. In particular the CaII lines were showing very strong absorption signatures never observed in the local ISM toward similarly nearby stars. From the comparison of the two first observations of these lines it became also clear that these lines were time variable. This lead to numerous observational campaigns showing that stable gas as well as infalling gas was present in the system. The concept of falling and evaporating bodies (FEBs) was born: unexpectedly, exocomets were observed before exoplanets ! The lifetime of the continuously produced gas being very short, it lead to a needed additional concept of a stable braking gas at rest relative to the system and able to stop all other species through collisions. The nature of this braking gas is still debated and its location unclear. The distance of the gas is shown to be very extended, some of it being at less than 1 AU, mainly from absorption studies and some at more than 100 AU from the star, mainly from the observation of emissions signatures. The nature, origin and composition of the gas seem to be due to either the evaporation of FEBs for the closer gas or to the evaporation of distant orbiting and evaporating bodies (OEBs) of all sizes including grains, for the more remote gas.

Vidal-Majar, A.

2014-09-01

117

Habitability of Planets Orbiting Binaries Consisting of Solar Mass Twins  

NASA Astrophysics Data System (ADS)

An important problem in astrobiology is the study of the potential habitability of planets orbiting binary stars. Theoretical and observational studies of circumbinary planets indicate that it is not uncommon for circumbinary planets to be located in the habitable zones surrounding main sequence binaries. However, it is also clear that the time evolution of stellar activity of the individual stars in close binaries is of primary concern for the habitability of planets. For example, planets orbiting active stars may lose the entirety of their water budget due to atmospheric mass loss; despite being in the standard radiative habitable zone. Alternatively, stars in some binaries may undergo a reduction in stellar activity due to tidal effects that cause the rotation of the stars to slow faster than single stars. Thereby, magneto-coronal activity is reduced to less aggressive levels, allowing circumbinary planets to maintain surface water. We summarize these effects, which we call the Binary Habitability Mechanism (BHM). We performed orbital integrations of circumbinary, Earth-like, planets and find that resonances play a particularly important role in the stability of habitable zone planets orbiting solar twin binaries in the 20-60 day period range, allowing for the possibility of several habitable planets orbiting some binaries. We present numerical simulations of the effects of colliding winds in binaries containing solar mass twins. We used stellar wind parameters based on solar like conditions for our 3D hydrodynamic simulations. We find devastating effects for close in planets, yet relatively mild stellar wind conditions exist within the circumbinary habitable zone.

Mason, Paul A.; Zuluaga, Jorge I.; Zhilkin, Andrey G.; Bisikalo, Dmitry V.

2015-01-01

118

Trajectories of Martian Habitability  

PubMed Central

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

2014-01-01

119

Physics and Chemistry of Circumstellar Dust Shells  

NASA Astrophysics Data System (ADS)

Part I. Setting the Stage: 1. Introduction; 2. Evolutionary status of dust-enshrouded objects; Part II. Theoretical Description of Circumstellar Dust Shells: 3. Theory of circumstellar dust shells; 4. The energy equation for matter; 5. Radiative transfer; 6. Interaction between gas and dust particles; 7. Extinction by dust grains and gas; 8. Approaches to the temperature equations; 9. Chemistry in thermodynamic equilibrium; 10. Gas-phase chemical composition; 11. Gas-solid chemical equilibria; 12. Growth of dust grains; 13. Formation of seed nuclei; 14. Moment equations; Part III. Applications: 15. Modeling of circumstellar dust shells; 16. Miras and long-period variables; 17. Mass loss formulae; 18. R Coronae Borealis stars; Part IV. Appendices; Bibliography; Index.

Gail, Hans-Peter; Sedlmayr, Erwin

2014-02-01

120

Physics and Chemistry of Circumstellar Dust Shells  

NASA Astrophysics Data System (ADS)

Part I. Setting the Stage: 1. Introduction; 2. Evolutionary status of dust-enshrouded objects; Part II. Theoretical Description of Circumstellar Dust Shells: 3. Theory of circumstellar dust shells; 4. The energy equation for matter; 5. Radiative transfer; 6. Interaction between gas and dust particles; 7. Extinction by dust grains and gas; 8. Approaches to the temperature equations; 9. Chemistry in thermodynamic equilibrium; 10. Gas-phase chemical composition; 11. Gas-solid chemical equilibria; 12. Growth of dust grains; 13. Formation of seed nuclei; 14. Moment equations; Part III. Applications: 15. Modeling of circumstellar dust shells; 16. Miras and long-period variables; 17. Mass loss formulae; 18. R Coronae Borealis stars; Part IV. Appendices; Bibliography; Index.

Gail, Hans-Peter; Sedlmayr, Erwin

2013-12-01

121

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

122

Learning How to Change Habits  

MedlinePLUS

... get ready. Then write the steps here. ___________________________________________ ___________________________________________ ___________________________________________ Learning How to Change Habits American Diabetes Association? ? 1–800–DIABETES ( ... Association, Inc. 10/13 Toolkit No. 4: Learning How to Change Habits continued Things to Do Examples Get ...

123

Encouraging Good Homework Habits.  

ERIC Educational Resources Information Center

Strategies for encouraging good homework habits include: plan daily quiet time for the family; schedule homework at times that work for the child and family; and help the child create a study area. Parents should resist doing the child's homework, discuss homework problems with teachers, limit homework to appropriate amounts of time, and be…

Villaire, Ted

2001-01-01

124

Radiological Habits Survey: Wylfa, 2009  

E-print Network

Radiological Habits Survey: Wylfa, 2009 2010 Environment Report RL 03/10 Cefas contract report C Radiological Habits Survey: Wylfa, 2009 C.J. Garrod, F.J. Clyne, J. Elliott and J.R. Tipple Peer reviewed by G, C. J., Clyne, F. C., Elliott, J., and Tipple, J.R., 2010. Radiological Habits Survey: Wylfa, 2009

125

Radiological Habits Survey: Wylfa, 2013  

E-print Network

Radiological Habits Survey: Wylfa, 2013 2014 Environment Report RL 03/14 Cefas contract report C6028 #12;This page has been intentionally left blank #12;Cefas Document Control Radiological Habits blank #12;Environment Report RL 03/14 Final report Radiological Habits Survey: Wylfa, 2013 C.J. Garrod

126

Radiological Habits Survey: Amersham, 2009  

E-print Network

Radiological Habits Survey: Amersham, 2009 2010 Environment Report RL 04/10 Cefas contract report C Radiological Habits Survey: Amersham, 2009 F.J. Clyne, C.J. Garrod and J. Elliott Peer reviewed by G.J. Hunt.C., Garrod, C.J. and Elliott, J., 2010. Radiological Habits Survey: Amersham, 2009. RL 04/10. Cefas

127

Radiological Habits Survey: Devonport, 2011  

E-print Network

Radiological Habits Survey: Devonport, 2011 2012 Environment Report RL 01/12 Cefas contract report Radiological Habits Survey: Devonport, 2011 F.J. Clyne, C.J. Garrod, V.E. Ly and P. Rumney Peer reviewed by G.J., Garrod, C.J., Ly, V.E. and Rumney, P., 2012. Radiological Habits Survey: Devonport, 2011. RL 01/12. Cefas

128

Radiological Habits Survey: Dungeness, 2010  

E-print Network

Radiological Habits Survey: Dungeness, 2010 2011 Environment Report RL 11/11 Cefas contract report Radiological Habits Survey: Dungeness, 2010 F.J. Clyne, C.J. Garrod, V.E. Ly, P. Rumney and J. Elliott Peer: Clyne, F.C., Garrod, C.J., Ly, V.E., Rumney, P., and Elliott, J., 2011. Radiological Habits Survey

129

Radiological Habits Survey: Heysham, 2011  

E-print Network

Radiological Habits Survey: Heysham, 2011 2012 Environment Report RL 02/12 Cefas contract report C Radiological Habits Survey: Heysham, 2011 C.J. Garrod, F.J. Clyne, V.E. Ly and P. Rumney Peer reviewed by G, C.J., Clyne, F.J., Ly, V.E. and Rumney, P., 2012. Radiological Habits Survey: Heysham, 2011. RL 02

130

Radiological Habits Survey: Derby, 2009  

E-print Network

Radiological Habits Survey: Derby, 2009 2010 Environment Report RL 05/10 Cefas contract report C Radiological Habits Survey: Derby, 2009 J. Elliott, F.J. Clyne and C.J. Garrod Peer reviewed by G.J. Hunt., Clyne, F.C. and Garrod, C.J., 2010. Radiological Habits Survey: Derby, 2009. RL 05/10. Cefas, Lowestoft

131

Radiological Habits Survey: Sizewell, 2010  

E-print Network

Radiological Habits Survey: Sizewell, 2010 2011 Environment Report RL 12/11 Cefas contract report C Radiological Habits Survey: Sizewell, 2010 C.J. Garrod, F.J. Clyne, P. Rumney, J. Elliott, C.A. Smedley and V, J., Smedley, C., and Ly, V.E., 2011. Radiological Habits Survey: Sizewell, 2010. RL 12/11. Cefas

132

Habitable planets with high obliquities  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

133

Isothermal Circumstellar Dust Shell Model for Teaching  

ERIC Educational Resources Information Center

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

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

2009-01-01

134

Photochemistry of carbon-rich circumstellar shells  

Microsoft Academic Search

The effect of ambient ultraviolet photons on the chemical structure of carbon-rich, circumstellar envelopes is investigated with a simple formulation of the time-dependent, photochemical rate equations valid for optically thick shells. Molecules injected into the shielded inner envelope are broken down when they reach the outer regions where ambient ultraviolet photons can penetrate. A quantitative description of the abundance variations

P. J. Huggins; A. E. Glassgold

1982-01-01

135

Trajectories of martian habitability.  

PubMed

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

Cockell, Charles S

2014-02-01

136

Direct imaging of habitable planets with ELTs  

NASA Astrophysics Data System (ADS)

ELTs will offer unprecedented angular resolution and collecting area, two of the essential ingredients for direct imaging and characterization of habitable exoplanets. If equipped with high performance AO system and coronagraph, ELTs will therefore be very powerful instruments for high contrast imaging of the immediate surroundings of nearby stars. An analysis of the expected performance of such a system, both from fundamental principles and extrapolations using current technologies developed for 10-m class telescopes, reveals that it will be able to image a large number of extrasolar planets. One of the most interesting finding of this analysis is that ELTs should be able to directly image potentially habitable planets in reflected light, and that reflected light imaging in the near-IR is easier than thermal emission imaging with an ELT (in part thanks to the ability to chose the most nearby stars as targets, as opposed to more distant young stars). While an Earth analog at 10pc would be at the very limit of detection even with a nearly optimal system (using a high sensitivity and high speed ExAO system), adopting a slightly broader definition of habitable planets including Super-Earths around late-type stars shows that detection and spectroscopic characterization of habitable planets will be within reach. For such targets, the reflected light contrast is more favorable and the planet is intrinsically brighter (since late type stars are more numerous, and can therefore be selected at small distance). The key to enable these detections is angular resolution, since the habitable zone around late type stars is very close to the star. An ExAO system for ELT should therefore use techniques optimal for high contrast imaging at a few diffraction limits from the central star. Such techniques are currently being developed in laboratories, and some of them are being deployed on existing telescopes: small inner working coronagraphs can now deliver full sensitivity images down to ˜1 ?/D, and new wavefront sensing techniques fully utilizing coherence over the entire pupil allow more than 10000x gain in sensitivity over conventional seeing-limited wavefront sensors. This science goal is complementary to direct imaging and characterization of habitable exoplanets from space, which favors F-G-K type stars at larger angular separation. Since no such space mission is planned for the near future (and will therefore likely not fly before ˜2025-2030), ground-based ELTs may in fact offer the first opportunity for detailed characterization of nearby habitable worlds.

Guyon, Olivier

2011-09-01

137

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

138

Expected Returns and Habit Persistence  

Microsoft Academic Search

Using a consumption-based asset pricing model with infinite-horizon nonlinear habit formation, Campbell and Cochrane (1999) show that low consumption in surplus of habit should forecast high expected returns. This article argues that the finite-horizon linear habit model also implies an inverse relation between expected returns and surplus consumption. This article also presents empirical evidence, which indicates that expected returns on

Yuming Li

2001-01-01

139

Stellar masers, circumstellar envelopes, and supernova remnants  

E-print Network

This paper reviews recent advances in the study or circumstellar masers and masers found toward supernova remnants. The review is organized by science focus area, including the astrophysics of extended stellar atmospheres, stellar mass-loss processes and outflows, late-type evolved stellar evolution, stellar maser excitation and chemistry, and the use of stellar masers as independent distance estimators. Masers toward supernova remnants are covered separately. Recent advances and open future questions in this field are explored.

Athol J. Kemball

2007-05-15

140

High contrast imaging polarimetry of circumstellar environments  

NASA Astrophysics Data System (ADS)

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

Canovas Cabrera, H.

2011-09-01

141

Habitable Planets Eclipsing Brown Dwarfs: Strategies for Detection and Characterization  

E-print Network

Given the very close proximity of their habitable zones, brown dwarfs 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 brown dwarfs depending on their maximum habitable orbital period (PHZ out). Habitable planets with PHZ out shorter than the useful duration of a night (e.g. 8-10 hrs) can be screened with 100 percent completeness from a single location and in a single night (near-IR). More luminous brown dwarfs require continuous monitoring for longer duration, e.g. from space or from a longitude-distributed network (one test scheduling achieved - 3 telescopes, 13.5 contiguous hours). Using a simulated survey of the 21 closest known brown dwarfs (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 percent, depending on our assumptions. We calculate that bro...

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

2013-01-01

142

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

143

Circumstellar material around young stars in Orion  

NASA Technical Reports Server (NTRS)

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

Odell, C. R.

1994-01-01

144

How Common are Habitable Planets?  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

145

Radiological Habits Survey: Sellafield, 2013  

E-print Network

Radiological Habits Survey: Sellafield, 2013 2014 Environment Report RL 02/14 Cefas contract report C6028 #12;This page has been intentionally left blank #12; Cefas Document Control Radiological #12;This page has been intentionally left blank #12;Environment Report RL 02/14 Radiological Habits

146

Developing Mathematical Habits of Mind  

ERIC Educational Resources Information Center

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

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

2010-01-01

147

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

148

Characteristics of Interstellar and Circumstellar Dust  

NASA Technical Reports Server (NTRS)

This paper will review our current knowledge of circumstellar and interstellar dust from an astronomical point of view. About half of the interstellar dust volume consists of amorphous silicates. The remainder has to be made up of an carbonaceous component such as graphite, amorphous carbon (i.e., soot), Polycyclic Aromatic Hydrocarbon molecules (PAHs), and/or organic grain mantles (i.e., mixed polymers). The observational evidence for these components will be reviewed and their relative importance assessed. The emphasis will be on recent observations using the Infrared Space Observatory. Most of these dust components are formed in the outflows from stars in the late stages of their evolution (i.e., red giants, planetary nebulae, novae, supergiants, Wolf Rayet stars, and supernovae). Indeed, observation of such objects indicate an even richer spectrum of stardust components, including also SiC, MgS, and aluminates and crystalline silicates. These observations will be briefly discussed. The stardust budget of the galaxy will be reviewed and the relative importance of the various birth sites assessed. Finally, in recent years, isotopic composition studies have shown that some circumstellar and interstellar dust grains have been incorporated into solar system bodies such as planetary dust particles and meteorites without totally losing their identity. Among the components identified are SiC, graphite, diamonds, PAHs, aluminum oxides, as well as various trace element carbides. Studies of this kind have opened up a new window on the composition and structure of interstellar dust. These different sources of information on interstellar and circumstellar dust will be briefly contrasted.

Tielens, A. G. G. M.; Young, Richard E. (Technical Monitor)

1997-01-01

149

Kinematic Dynamo In Turbulent Circumstellar Disks  

NASA Technical Reports Server (NTRS)

Many circumstellar disks associated with objects ranging from protoplanetary nebulae, to accretion disks around compact stars allow for the generation of magnetic fields by an (alpha)omega dynamo. We have applied kinematic dynamo formalism to geometrically thin accretion disks. We calculate, in the framework of an adiabatic approximation, the normal mode solutions for dynamos operating in disks around compact stars. We then describe the criteria for a viable dynamo in protoplanetary nebulae, and discuss the particular features that make accretion disk dynamos different from planetary, stellar, and galactic dynamos.

Stepinski, T.

1993-01-01

150

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

151

The Structure of Brown Dwarf Circumstellar Disks  

E-print Network

We present synthetic spectra for circumstellar disks that are heated by radiation from a central brown dwarf. Under the assumption of vertical hydrostatic equilibrium, our models yield scaleheights for brown dwarf disks in excess of three times those derived for classical T Tauri (CTTS) disks. If the near-IR excess emission observed from brown dwarfs is indeed due to circumstellar disks, then the large scaleheights we find could have a significant impact on the optical and near-IR detectability of such systems. Our radiation transfer calculations show that such highly flared disks around brown dwarfs will result in a large fraction of obscured sources due to extinction of direct starlight by the disk over a wide range of sightlines. The obscured fraction for a 'typical' CTTS is less than 20%. We show that the obscured fraction for brown dwarfs may be double that for CTTS, but this depends on stellar and disk mass. We also comment on possible confusion in identifying brown dwarfs via color-magnitude diagrams: edge-on CTTS display similar colors and magnitudes as a face-on brown dwarf plus disk systems.

Christina Walker; Kenneth Wood; C. J. Lada; Thomas Robitaille; J. E. Bjorkman; Barbara Whitney

2004-03-11

152

A 'dry' condensation origin for circumstellar carbonates.  

PubMed

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

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

2005-10-20

153

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

154

Engineering the seven habits [project management  

Microsoft Academic Search

The Seven Habits of Highly Effective People by Steven Covey (1989), provides an excellent framework for creating an effective engineering culture. This paper explores the seven habits specifically in the context of conducting an engineering project. Following these habits leads to results that consistently improve the chances of meeting customer expectations and achieving business objectives. This paper overviews each habit,

D. H. Holly

1998-01-01

155

Delegation: developing the habit.  

PubMed

Often, individuals take personal delegation skills for granted and assume the presence of expertise with the practice of delegation, which may not be the case. Those assumptions can be found at both ends of the process, with the manager and the employee. Every time a manager places an employee in a job and gives him or her a job description or a set of instructions, the manager has delegated. The manager has placed someone in a position to perform operations for which ultimately the manager is responsible. Delegation is both a process and a condition. The process is the act of assigning work to an employee; the condition of delegating a job is a thorough and mutual understanding between the supervisor and the employee of specific results and methods by which these results can be achieved. The condition goes far beyond the simple process of assigning a job. The point at which many managers fail in delegating is in neglecting to move past the process and take the required steps to establish a true condition of delegation. Failure to delegate is the leading cause of managers retarding their professional growth. In the case of a workaholic--someone who fails to learn the value of delegation--the job soon becomes too much, and the effectiveness of the department may suffer. By reducing the burden of technical duties and busy work, managers will find that it is possible to be more effective and actually spend more time managing. A number of the reasons why managers fail to delegate are complex and subconscious, such as insecurity, fear of competition and even fear of not being recognized for accomplishments achieved. Other reasons for failing to delegate are habit and shortages of staff members or time. Delegation is an investment in time. The eventual gain from such an investment, which may temporarily cause the department to fall further behind during a training period, outweighs the costs. The manager is the final authority in such duties as approval, recommendations and implementations. Remember that to delegate authority does not mean to delegate ultimate responsibility. Only the manager should bear the burden of responsibilities that directly affect his or her career. One of the most common mistakes in the process of delegating is to turn an employee loose on a job with inadequate instruction. Too often this is caused by lack of time. Strictly speaking, when managers assign tasks to employees, they are delegating the authority to perform the task. However, all responsibility for the completion of the task remains with the manager. In most instances, responsibility for the failure of a delegated project lies with the manager, not the employee. While some failure is to be expected, it can be minimized by proper evaluation of the situation and proper communication. Delegation is a calculated risk. The manager should be willing to take a risk to see if an employee does have the skills and ability to perform the specific task. How else will the manager ever know? Developing a strong habit of delegation will lead to development of an effective and efficient staff and department. Delegation will serve not only the organization well, but also managers throughout their careers. PMID:11499078

Duehring, G L

2001-01-01

156

Galactic Habitable Orbits  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

157

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

2000-01-01

158

Modeling circumstellar envelope with advanced numerical codes  

NASA Astrophysics Data System (ADS)

We propose a modeling study on the formation and evolution of the Circumstellar Envelopes (CSEs) of a sample of selected radio-loud objects, based on an innovative interaction between two codes widely used by the scientific community, but in different fields. CLOUDY (Ferland et al. 1998) is a widely used code to model the spectral energy distribution (SED) of the several objects characterized by clouds of gas heated and ionized by a central object. CosmoMC (Lewis & Bridle 2002) instead is usually used for exploring cosmological parameter space. We investigate here on the exploitation of the sampling performance of the Markov-Chain Monte-Carlo (MCMC) engine of CosmoMC to search for a best fit model of the considered objects through the spectral synthesis capacity of CLOUDY.

Procopio, P.; De Rosa, A.; Burigana, C.; Umana, G.; Trigilio, C.

2011-06-01

159

HL Tauri and its circumstellar disk  

NASA Technical Reports Server (NTRS)

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

Cohen, M.

1983-01-01

160

Exotic Earths: Forming Habitable Worlds with Giant Planet Migration  

E-print Network

Close-in giant planets (e.g. ``Hot Jupiters'') are thought to form far from their host stars and migrate inward, through the terrestrial planet zone, via torques with a massive gaseous disk. Here we simulate terrestrial planet growth during and after giant planet migration. Several-Earth mass planets also form interior to the migrating Jovian planet, analogous to recently-discovered ``Hot Earths''. Very water-rich, Earth-mass planets form from surviving material outside the giant planet's orbit, often in the Habitable Zone and with low orbital eccentricities. More than a third of the known systems of giant planets may harbor Earth-like planets.

Sean N. Raymond; Avi M. Mandell; Steinn Sigurdsson

2006-09-08

161

Circumstellar Disks in the IC 348 Cluster  

E-print Network

We report the results of the first sensitive L-band (3.4 micron) imaging survey of the young IC 348 cluster in Perseus. In conjunction with previously acquired JHK (1.25, 1.65, 2.2 micron) observations, we use L-band data to obtain a census of the circumstellar disk population to m_K=m_L<=12.0 in the central 110 square arcmin region of the cluster. An analysis of the JHKL colors of 107 sources indicates that 65% +/- 8% of the cluster membership possesses (inner) disks. This fraction is lower than those (86% +/- 8% and 80% +/- 7%) obtained from similar JHKL surveys of the younger NGC 2024 and Trapezium clusters, suggesting that the disk fraction in clusters decreases with cluster age. Sources with circumstellar disks in IC 348 have a median age of 0.9 Myr, while the diskless sources have a median age of 1.4 Myr, for a cluster distance of 320 pc. Although the difference in the median ages between the two populations is only marginally significant, our results suggest that over a timescale of 2 - 3 Myr, more than a third of the disks in the IC 348 cluster disappear. Moreover, we find that at a very high confidence level, the disk fraction is a function of spectral type. All stars earlier than G appear diskless, while stars with spectral types G and later have a disk fraction ranging between 50% - 67%, with the latest type stars having the higher disk fraction. This suggests that the disks around stars with spectral types G and earlier have evolved more rapidly than those with later spectral types. The L-band disk fraction for sources with similar ages in both IC 348 and Taurus is the same, within the errors, suggesting that, at least in clusters with no O stars, the disk lifetime is independent of environment.

Karl E. Haisch Jr.; Elizabeth A. Lada; Charles J. Lada

2001-01-26

162

Finding Habitable Planets Around the Nearest Stars  

NASA Astrophysics Data System (ADS)

The discovery of the first 700 extrasolar planets have had a profound impact on science and society. The 2000 Decadal Survey of Astronomy & Astrophysics cites the discovery of extrasolar planets as the most important advance of the previous decade. The 2010 Decadal Survey cites extrasolar planets as one of the three pillars of modern astrophysics, and explicitly states that the discovery of potentially habitable planets around nearby stars is the highest priority for the next decade. Most of the planets that have been discovered orbiting nearby stars are massive gas giants found with Doppler velocity systems that have achieved 3 to 10 m/s. This first generation of exoplanets had amplitudes of 50 m/s or more, and could be detected with sparse sampling. Terrestrial mass and super-earth planets in habitable 1 AU orbits around G dwarfs have Doppler amplitudes of less than 0.5 m/s, and are currently undetectable. Due to their lower mass and brightness, the habitable liquid water zone around M dwarfs is at 0.1 to 0.2 AU, with corresponding Doppler velocity amplitudes of 2 to 5 m/s. These planets are typically in multiple planet systems in which several planets have similar amplitudes, leading to complex Doppler velocity signals. These planets can be detected with high cadence observations that achieve state-of-the-art precision of 1 m/s. While M dwarfs constitute 70% of the nearest stars, they are significantly fainter than nearby G & K dwarfs, and require large telescopes to reach 1 m/s precision. We have built the first American Doppler velocity system that produces 1 m/s precision. The Planet Finding Spectrometer (PFS) on Magellan has been custom built for precision velocity measurements. Compared to HIRES on Keck, PFS is mechanically and thermally stabilized, has triple the throughput, operates at higher resolution, and had 50% greater sampling. PFS on Magellan is slightly faster than HIRES on Keck in spite of the difference in aperture, 6.5-m vs 10-m. We are currently receiving ~50 nights per year on Magellan/PFS to target the nearest M dwarfs with high cadence observations. Over the next 3 years we will survey the nearest 200 M dwarfs with sufficient precision and cadence to detect terrestrial mass and super- earth planets in the habitable zone of these stars. After just two high cadence observing runs we already have candidates. Over the past quarter century our planet surveys, initially at Lick and later at Keck and the AAT, have had a broad societal and scientific impact, including the discovery of half of the known planets orbiting nearby stars. Our work has been credited with providing the motivation for the new disciplines of astrobiology and extrasolar planet studies. All the Iodine precision velocity systems in the world are based on our original system on the Lick 3-m (Butler et al. 1996). For us the PFS/Magellan system is the culmination of 25 years of work, leading to the detection of potentially habitable planets.

Butler, R.

163

EXCEDE: The Exoplanetary Circumstellar Environment And Disk Explorer Utilizing A Phase Induced Amplitude Apodized Coronagraphic Telescope For High Contrast Imaging Of Circumstellar Planet-forming Environments  

NASA Astrophysics Data System (ADS)

We describe the Exoplanetary Circumstellar Environment and Disk Explorer (EXCEDE) SMEX mission to directly image starlight-scattering circumstellar material in the planet-forming regions of stars exhibiting thermal infrared emission above their stellar photospheric levels (a signpost of planetary systems in formation). EXCEDE will provide contrast-limited scattered-light detection sensitivities 100 to 1000 times more sensitive than the HST and JWST coronagraphs at a smaller inner working angle, enabling the exploration and characterization of exoplanetary circumstellar disk systems in currently inaccessible observational domains. Utilizing a laboratory-demonstrated high-performance Phase Induced Amplitude Apodized Coronagraph (PIAA-C), integrated with a small (0.5 meter diameter) unobscured aperture visible-light telescope, EXCEDE will provide unrivaled disk-to-star imaging contrast ratios of < 1:10,000,000 at a 1 lambda/d inner working angle of 0.2" with 200 mas spatial resolution at 0.4 microns. Such unprecedented spatially-resolved circumstellar disk images will enable determinations of disk characteristics (mass, geometry, surface brightness, grain properties) for stars over a wide range of stellar mass and age, providing a unique and comprehensive dataset to understand the formation and evolution of extrasolar planetary systems. Concomitantly, EXCEDE will provide unparalleled imagery of those rare debris disks previously resolved with inferior capabilities. These "Rosetta stones" are the basis of our current understanding of planetary disk systems and EXCEDE/PIAA-C observations will overcome current limitations that thus-far have resulted in significant model degeneracies. EXCEDE will also directly image and characterize extrasolar giant planets with orbital distances as small as 1.5 AU and disk sub-structures influenced by co-orbiting planets - for the first time within the terrestrial planet zone (< 5 AU) around the nearest targets. EXCEDE is a science-driven technology pathfinder and demonstrator for subsequent planet-finding and characterization missions that will also provide future missions (e.g., JWST/MIRI & TPF-C) well-honed targets sets for follow-on and multi-wavelength investigations.

Greene, Thomas P.; Schneider, G.; Science, EXCEDE; Mission Team

2007-12-01

164

Instabilities in Circumstellar Discs Charles F. Gammie 1  

E-print Network

Instabilities in Circumstellar Discs Charles F. Gammie 1 Isaac Newton Institute, 20 Clarkson Rd is governed by angular momentum transport; without torques the disc gas would remain in orbit and not accrete

Gammie, Charles F.

165

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

166

Magnetic Fields And Developing Asymmetries In Circumstellar Masers  

NASA Astrophysics Data System (ADS)

Maser emission occurs in different regions of the circumstellar envelopes (CSEs) of evolved stars and can be studied at high angular resolution using radio interferometers. These masers are useful probes of the dynamics and kinematics of the outflow from AGB stars. Moreover, masers can be important tracers of the magnetic field strength and morphology at various distances from the central stars. It is expected that the magnetic field plays an important role in transforming spherically symmetric asymptotic giant branch (AGB) stars into a-spherical planetary nebulae (PNe). Theoretical modeling indicated that magnetically collimated jets may be responsible for the formation of the a-spherical PNe. Water fountain sources are a class of post-AGB objects in which H2O masers indicate high velocity collimated jets. Our radio interferometric observations indicate that asymmetries are also present in the OH maser region of the envelope. We performed kinematical reconstruction in order to understand the distribution of OH masers in the CSEs of these stars. Our results show that the OH masers could have either equatorial or bi-conical distribution. Additionally, the observations reveal significant field strength for the OH maser region of these objects, which show the possible role of the magnetic field in collimating the CSEs. At distances close to the central stars, between the photosphere and the dust formation zone, SiO masers occur. SiO maser polarimetry has been performed for Mira variables and supergiants and seems to indicate dynamically significant and ordered magnetic fields. We extended these studies and performed VLBA SiO maser polarization observations of objects with more extreme mass-loss, in order to understand the origin of the transition between the AGB and PNe. These observations will enable us to understand the SiO emission mechanisms and possibly distinguish between competing models on the origin of the SiO maser polarization.

Amiri, Nikta; Vlemmings, W.; van Langevelde, H.; Kemball, A.

2011-05-01

167

Breastfeeding FAQs: Your Eating and Drinking Habits  

MedlinePLUS

... Checkups: What to Expect Ebola: What to Know Breastfeeding FAQs: Your Eating and Drinking Habits KidsHealth > Parents > Growth & Development > Feeding & Eating > Breastfeeding FAQs: Your Eating and Drinking Habits Print A ...

168

[Dietary habits and cardiovascular diseases].  

PubMed

Cardiovascular diseases are a major public health problem worldwide. They are the main cause of death in industrialized countries, while the mortality associated with cardiovascular disease is increasing in less developed countries. The modifiable risk factors for cardiovascular disease are cigarette smoking, hypertension, hyperlipidemia, diabetes mellitus and obesity. Obesity has been recorded in 10%-25% of the population, indicating that poor or inappropriate diet is one of the most common causes of cardiovascular disease. Unhealthy dietary habits including place and way of taking meals, number of daily meals and excessive salt intake from processed foods also contribute to body mass gain. In the present study, dietary habits were assessed in cardiovascular patients versus control group by use of Dietary Habits Questionnaire. Study results showed a statistically significantly higher (P < 0.05) prevalence of inappropriate eating habits in cardiovascular patients (lower number of daily meals, more often skipping breakfast and having dinner) than in control group. In conclusion, many lifestyle and individual behavior modifications are needed in most patients with or at a high risk of cardiovascular disease. PMID:20649073

Nola, Iskra Alexandra; Doko Jelini?, Jagoda; Bergovec, Mijo; Ruzi?, Alen; Persi?, Viktor

2010-05-01

169

Drug Advertising and Health Habit  

Microsoft Academic Search

We examine the effect of direct-to-consumer advertising (DTCA) of drug treatment on an important health habit, physical exercise. By learning the existence of a new drug treatment via DTCA, rational consumers may become careless about maintaining healthy lifestyles. Using the National Health Insurance Survey (NHIS) and MSA-level DTCA data, we find that the DTCA related to four chronic conditions --

Toshiaki Iizuka; Ginger Zhe Jin

2005-01-01

170

Encouraging the Lifetime Reading Habit.  

ERIC Educational Resources Information Center

Educators must accept the challenge of encouraging the lifetime reading habit in school. Students who are surrounded with books, newspapers, magazines, and other materials will be tempted to browse and to read from these sources. When selecting materials for the classroom, educators should work closely with the library media specialist who is…

Sanacore, Joseph

171

Habitable Planet Formation in Binary-Planetary Systems  

E-print Network

Recent radial velocity observations have indicated that Jovian-type planets can exist in moderately close binary star systems. Numerical simulations of the dynamical stability of terrestrial-class planets in such environments have shown that, in addition to their giant planets, these systems can also harbor Earth-like objects. In this paper, we study the late stage of terrestrial planet formation in such binary-planetary systems, and present the results of the simulations of the formation of Earth-like bodies in their habitable zones. We consider a circumprimary disk of Moon- to Mars-sized objects and numerically integrate the orbits of these bodies at the presence of the Jovian-type planet of the system and for different values of the mass, semimajor axis, and orbital eccentricity of the secondary star. Results indicate that, Earth-like objects, with substantial amounts of water, can form in the habitable zone of the primary star. Simulations also indicate that, by transferring angular momentum from the secondary star to protoplanetary objects, the giant planet of the system plays a key role in the radial mixing of these bodies and the water contents of the final terrestrial planets. We will discuss the results of our simulation and show that the formation of habitable planets in binary-planetary systems is more probable in binaries with moderate to large perihelia.

Nader Haghighipour; Sean N. Raymond

2007-02-27

172

Habitability potential of icy moons: a comparative study  

NASA Astrophysics Data System (ADS)

Looking for habitable conditions in the outer solar system our research focuses on the natural satellites rather than the planets themselves. Indeed, the habitable zone as traditionally defined may be larger than originally con-ceived. The strong gravitational pull caused by the giant planets may produce enough energy to sufficiently heat the interiors of orbiting icy moons. The outer solar system satellites then provide a conceptual basis within which new theories for understanding habitability can be constructed. Measurements from the ground but also by the Voyager, Galileo and the Cassini spacecrafts revealed the potential of these satellites in this context, and our understanding of habitability in the solar system and beyond can be greatly enhanced by investigating several of these bodies together [1]. Their environments seem to satisfy many of the "classical" criteria for habitability (liquid water, energy sources to sustain metabolism and chemical compounds that can be used as nutrients over a period of time long enough to allow the development of life). Indeed, several of the moons show promising conditions for habitability and the de-velopment and/or maintenance of life. Europa, Callisto and Ganymede may be hiding, under their icy crust, putative undersurface liquid water oceans [3] which, in the case of Europa [2], may be in direct contact with a silicate mantle floor and kept warm by tidally generated heat [4]. 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. Titan's rigid crust and the probable existence of a subsurface ocean create an analogy with terrestrial-type plate tectonics, at least surficial [5], while Enceladus' plumes find an analogue in gey-sers. As revealed by Cassini the liquid hydrocarbon lakes [6] distributed mainly at polar latitudes on Titan are ideal isolated environments to look for biomarkers. Currently, for Titan and Enceladus, geophysical models try to explain the possible existence of an oceanic layer that decouples the mantle from the icy crust. If the silicate mantles of Eu-ropa and Ganymede and the liquid sources of Titan and Enceladus are geologically active as on Earth, giving rise to the equivalent of hydrothermal systems, the simultaneous presence of water, geodynamic interactions, chemical en-ergy sources and a diversity of key chemical elements may fulfill the basic conditions for habitability. Titan has been suggested to be a possible cryovolcanic world due to the presence of local complex volcanic-like geomorphol-ogy and the indications of surface albedo changes with time [7,8]. Such dynamic activity that would most probably include tidal heating, possible internal convection, and ice tectonics, is believed to be a pre-requisite of a habitable planetary body as it allows the recycling of minerals and potential nutrients and provides localized energy sources. In a recent study by Sohl et al. [2013], we have shown that tidal forces are a constant and significant source of inter-nal deformation on Titan and the interior liquid water ocean can be relatively warm for reasonable amounts of am-monia concentrations, thus completing the set of parameters needed for a truly habitable planetary body. Such habi-tability indications from bodies at distances of 10 AU, are essential discoveries brought to us by space exploration and which have recently revolutionized our perception of habitability in the solar system. In the solar system's neighborhood, such potential habitats can only be investigated with appropriate designed space missions, like JUICE-Laplace (JUpiter ICy moon Explorer) for Ganymede and Europa [9]. JUICE is an ESA mission to Jupiter and its icy moons, recently selected to launch in 2022. References: [1] Coustenis, A., Encrenaz, Th., in "Life Beyond Earth : the search for habitable worlds in the Universe", Cambridge Univ. Press, 2013. [2] Patterson, G.W., et al.: AGU P41F-09, 2011. [3]

Solomonidou, Anezina; Coustenis, Athena; Encrenaz, Thérèse; Sohl, Frank; Hussmann, Hauke; Bampasidis, Georgios; Wagner, Frank; Raulin, François; Schulze-Makuch, Dirk; Lopes, Rosaly

2014-05-01

173

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

174

Interferometric Imaging of Circumstellar Disks with OVRO  

NASA Astrophysics Data System (ADS)

We are conducting an intensitve multi-species imaging study of two T Tauri and two Herbig Ae stars with the Owens Valley Millimeter Array. Interferometric images of several species in each of the important chemical families (C-, N-, O-, and S-bearing), including a number of isotopic variants, have been acquired. Even at moderate resolution (5") there appear to be interesting morphological differences between species expected to follow different (photo)chemical paths. The HCN velocity structure is similar to that seen in CO(2-1) showing that HCN participates in the same disk rotation. The integrated intensity map of HCN, however, shows a double peaked morphology suggestive of depletion of HCN in the inner disk. The H13CO+ emission provides an important lower bound to the gas fractional ionization of a few 10-10. The first detection of DCN in this kind of object has made possible a determination of the critical D/H ratio (DCN/HCN) in the circumstellar gas. At present, the data provides an approximate value of the D/H ratio of 0.01 since even H13CN(1-0) is optically thick, judging by its three hyperfine components. Still, this very high D/H ratio is comparable to those in comets, and suggests an evolutionary history in which cometary materials remain at very low temperatures throughout their assemblage and for the bulk of their lives.

Qi, Charlie; Blake, Geoffrey A.; Sargent, Anneila I.

1999-10-01

175

The seven habits of highly defective people  

Microsoft Academic Search

Steven Covey had tremendous success with his seven habits for success in business in particular and life in general. This article takes a light-hearted, irreverent look at analyzing the habits of the people who do not have such great prosperity. Chronically less than successful people suffer from seven diseases (or habits) including: playing the victim, failure to see the bigger

Ken Matejka; Richard J. Dunsing; Bryce Walat

1998-01-01

176

Radiological Habits Survey: Sellafield Review, 2010  

E-print Network

Radiological Habits Survey: Sellafield Review, 2010 2011 Environment Report RL 13/11 Cefas contract Radiological Habits Survey: Sellafield Review, 2010 Shellfish consumption and intertidal occupancy review F, P., Smedley, C.A., and Ly, V.E., 2011. Radiological Habits Survey: Sellafield Review, 2010. RL 13

177

Radiological Habits Survey: Sellafield Review, 2011  

E-print Network

Radiological Habits Survey: Sellafield Review, 2011 2012 Environment Report RL 05/12 Cefas contract Radiological Habits Survey: Sellafield Review, 2011 Shellfish consumption and intertidal occupancy review F., 2012. Radiological Habits Survey: Sellafield Review, 2011. RL 05/12. Cefas, Lowestoft A copy can

178

Radiological Habits Survey: Sellafield Review, 2012  

E-print Network

Radiological Habits Survey: Sellafield Review, 2012 2013 Environment Report RL 04a/13 Cefas Final report Radiological Habits Survey: Sellafield Review, 2012 Aquatic pathways review G.P. Papworth, C.J., Ly, V.E., and Dewar, A., 2013. Radiological Habits Survey: Sellafield Review, 2012. RL 04a/13

179

Climate Stability of Habitable Earth-like Planets  

E-print Network

The carbon-silicate cycle regulates the atmospheric $CO_2$ content of terrestrial planets on geological timescales through a balance between the rates of $CO_2$ volcanic outgassing and planetary intake from rock weathering. It is thought to act as an efficient climatic thermostat on Earth and, by extension, on other habitable planets. If, however, the weathering rate increases with the atmospheric $CO_2$ content, as expected on planets lacking land vascular plants, the carbon-silicate cycle feedback can become severely limited. Here we show that Earth-like planets receiving less sunlight than current Earth may no longer possess a stable warm climate but instead repeatedly cycle between unstable glaciated and deglaciated climatic states. This has implications for the search for life on exoplanets in the habitable zone of nearby stars.

Menou, Kristen

2014-01-01

180

Environmental control system for Habitable-zone Planet Finder (HPF)  

NASA Astrophysics Data System (ADS)

HPF is an ultra-stable, precision radial velocity near infrared spectrograph with a unique environmental control scheme. The spectrograph will operate at a mid-range temperature of 180K, approximately half way between room temperature and liquid nitrogen temperature; it will be stable to sub -milli-Kelvin(mK) levels over a calibration cycle and a few mK over months to years. HPF's sensor is a 1.7 micron H2RG device by Teledyne. The environmental control boundary is a 9 m2 thermal enclosure that completely surrounds the optical train and produces a near blackbody cavity for all components. A large, pressure - stabilized liquid nitrogen tank provides the heat sink for the system via thermal straps while a multichannel resistive heater control system provides the stabilizing heat source. High efficiency multi-layer insulation blanketing provides the outermost boundary of the thermal enclosure to largely isolate the environmental system from ambient conditions. The cryostat, a stainless steel shell derived from the APOGEE design, surrounds the thermal enclosure and provides a stable, high quality vacuum environment. The full instrument will be housed in a passive 'meat -locker' enclosure to add a degree of additional thermal stability and as well as protect the instrument. Effectiveness of this approach is being empirically demonstrated via long duration scale model testing. The full scale cryostat and environmental control system are being constructed for a 2016 delivery of the instrument to the Hobby-Eberly Telescope. This report describes the configuration of the hardware and the scale-model test results as well as projections for performance of the full system.

Hearty, Fred; Levi, Eric; Nelson, Matt; Mahadevan, Suvrath; Burton, Adam; Ramsey, Lawrence; Bender, Chad; Terrien, Ryan; Halverson, Samuel; Robertson, Paul; Roy, Arpita; Blank, Basil; Blanchard, Ken; Stefansson, Gudmundur

2014-07-01

181

A model of habitability within the Milky Way galaxy.  

PubMed

We present a model of the galactic habitable zone (GHZ), described in terms of the spatial and temporal dimensions of the Galaxy that may favor the development of complex life. The Milky Way galaxy was modeled using a computational approach by populating stars and their planetary systems on an individual basis by employing Monte Carlo methods. We began with well-established properties of the disk of the Milky Way, such as the stellar number density distribution, the initial mass function, the star formation history, and the metallicity gradient as a function of radial position and time. We varied some of these properties and created four models to test the sensitivity of our assumptions. To assess habitability on the galactic scale, we modeled supernova rates, planet formation, and the time required for complex life to evolve. Our study has improved on other literature on the GHZ by populating stars on an individual basis and modeling Type II supernova (SNII) and Type Ia supernova (SNIa) sterilizations by selecting their progenitors from within this preexisting stellar population. Furthermore, we considered habitability on tidally locked and non-tidally locked planets separately and studied habitability as a function of height above and below the galactic midplane. In the model that most accurately reproduces the properties of the Galaxy, the results indicate that an individual SNIa is ?5.6× more lethal than an individual SNII on average. In addition, we predict that ?1.2% of all stars host a planet that may have been capable of supporting complex life at some point in the history of the Galaxy. Of those stars with a habitable planet, ?75% of planets are predicted to be in a tidally locked configuration with their host star. The majority of these planets that may support complex life are found toward the inner Galaxy, distributed within, and significantly above and below, the galactic midplane. PMID:22059554

Gowanlock, M G; Patton, D R; McConnell, S M

2011-11-01

182

Maximum number of habitable planets at the time of Earth's origin: new hints for panspermia?  

PubMed

New discoveries have fuelled the ongoing discussion of panspermia, i.e. the transport of life from one planet to another within the solar system (interplanetary panspermia) or even between different planetary systems (interstellar panspermia). The main factor for the probability of interstellar panspermia is the average density of stellar systems containing habitable planets. The combination of recent results for the formation rate of Earth-like planets with our estimations of extrasolar habitable zones allows us to determine the number of habitable planets in the Milky Way over cosmological time scales. We find that there was a maximum number of habitable planets around the time of Earth's origin. If at all, interstellar panspermia was most probable at that time and may have kick-started life on our planet. PMID:12967269

von Bloh, Werner; Franck, Siegfried; Bounama, Christine; Schellnhuber, Hans-Joachim

2003-04-01

183

Food habits of blue grouse  

USGS Publications Warehouse

The food habits of Blue Grouse vary from a simple winter diet that is made up predominantly of coniferous needles to a complex diet during the summer months, characterized by great variety of foods including green leaves, fruits and seeds, flowers, animal matter and coniferous needles. The spring and fall, which represent the transition periods between these two, are characterized by feeding habits that are generally intermediate. The diets of the two species of Blue Grouse, Dendrugapus obscurus and Dendragapus juliginosus, are quite similar as far as major types of food are concerned, but they differ considerably in the species that are taken. Such differences reflect differences in the vegetation within the ecologic and geographic ranges occupied by the two species.

Stewart, R.E.

1944-01-01

184

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

185

Development of a Habitable Planet  

NSDL National Science Digital Library

In this lesson, students investigate the origin of the elements, the process of planet formation, the evolution of life on Earth, and the conditions necessary for life as we know it. Using multimedia resources and a classroom activity, students identify and sequence the major events that caused Earth to develop into the planet we know, understand where the ingredients for Earth originated, including the conditions necessary for life, and consider the likelihood of other habitable worlds.

2005-01-01

186

Habits of highly effective dentists.  

PubMed

While stress is pervasive in the world today, and particularly in the dental office, coping strategies can counteract it. This paper discusses the personality features of the hardy dentist; the fact that stress and its effects depend largely on individual perception of stressors; and five habits to develop for stress reduction: seeking information, taking direct action, inhibiting action, engaging intrapsychic efforts and calling on others. PMID:7523616

Mazey, K A

1994-02-01

187

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

188

What Makes a World Habitable?  

NSDL National Science Digital Library

This is a lesson about characteristics necessary for life. Learners will identify the top candidates for life in the solar system by examining Habitability Cards, which discuss each planet and the six large moons in terms of water temperature, atmosphere, energy, and nutrients. A math extension is provided on the Inverse Square Law. Includes background reading for teachers, student activity guide, reflection questions, and blackline masters. This is activity 3 of 5 in the educators guide, Astrobiology in your Classroom: Life on Earth..and Elsewhere?

189

Radiological Habits Survey: Hinkley Point, 2010  

E-print Network

Radiological Habits Survey: Hinkley Point, 2010 2011 Environment Report RL 01/11 Cefas contract Radiological Habits Survey: Hinkley Point, 2010 F.J. Clyne, C.J. Garrod, P. Rumney, L.M. Hughes and V.E. Ly be cited as: Clyne, F.C., Garrod, C.J., Rumney, P., Hughes, L.M., and Ly, V.E., 2011. Radiological Habits

190

Space station group activities habitability module study  

NASA Technical Reports Server (NTRS)

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 Research Phase, architectural program and habitability design guidelines are specified. In the Schematic Design Phase, a range of alternative concepts is described and illustrated with drawings, scale-model photographs and design analysis evaluations. Recommendations are presented on the internal architectural, configuration of the Space Station Habitability Module for such functions as the wardroom, galley, exercise facility, library and station control work station. The models show full design configurations for on-orbit performance.

Nixon, David

1986-01-01

191

Supernova spectra below strong circumstellar interaction  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

192

The gas temperature in circumstellar disks: effects of dust settling  

E-print Network

The gas temperature in circumstellar disks: effects of dust settling F. Faas, G.J. van Zadelhoff, E systems. One of the central questions concerning these disks are their density and temperature distributions. The disk gas-temperature (T ¢¡¢£ ) is in general assumed to be equal to the dust-temperature (T

Zadelhoff, Gerd-Jan van

193

Hot Molecular Circumstellar Disk around Massive Protostar Orion Source I  

E-print Network

We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidate. We detected two ortho-H$_{2}$O lines at 321 GHz ($10_{2,9}$-$9_{3,6}$) and 336 GHz ($\

Hirota, Tomoya; Kurono, Yasutaka; Honma, Mareki

2013-01-01

194

The photochemistry of carbon-rich circumstellar shells  

Microsoft Academic Search

The effect of ambient ultraviolet photons on the chemical structure of carbon-rich, circumstellar envelopes is investigated with a simple formulation of the time-dependent, photochemical rate equations valid for optically thick shells. Molecules injected into the shielded inner envelope are broken down when they reach the outer regions where ambient ultraviolet photons can penetrate. A quantitative description of the abundance variations

P. J. Huggins; A. E. Glassgold

1982-01-01

195

Circumstellar Masers in the Galactic center Lor ant Sjouwerman  

E-print Network

with IRAS colors characteristic of CSE's, many double peaked 1612 MHz OH masers, the so-called OH/IR stars will be discussed, with the emphasis on masers in OH/IR stars. Using the masers, some recent clues about, the new VERA array will be presented. Keywords: Masers, Galactic center, AGB stars, Circumstellar matter

Sjouwerman, Loránt

196

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

E-print Network

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 ($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.

Nader Haghighipour

2007-11-06

197

Dietary habits and esophageal cancer.  

PubMed

Cancer of the esophagus is an underestimated, poorly understood, and changing disease. Its overall 5-year survival is less than 20%, even in the United States, which is largely a function of a delay in diagnosis until its more advanced stages. Additionally, the epidemiologic complexities of esophageal cancer are vast, rendering screening and prevention limited at best. First, the prevalence of esophageal cancer is unevenly distributed throughout the world. Second, the two histological forms (squamous cell and adenocarcinoma) vary in terms of their geographic prevalence and associated risk factors. Third, some populations appear at particular risk for esophageal cancer. And fourth, the incidence of esophageal cancer is in continuous flux among groups. Despite the varied prevalence and risks among populations, some factors have emerged as consistent associations while others are only now becoming more fully recognized. The most prominent, scientifically supported, and long-regarded risk factors for esophageal cancer are tobacco, alcohol, and reflux esophagitis. Inasmuch as the above are regarded as important risk factors for esophageal cancer, they are not the sole contributors. Dietary habits, nutrition, local customs, and the environment may be contributory. Along these lines, vitamins, minerals, fruits, vegetables, meats, fats, salted foods, nitrogen compounds, carcinogens, mycotoxins, and even the temperature of what we consume are increasingly regarded as potential etiologies for this deadly although potentially preventable disease. The goal of this review is to shed light on the less known role of nutrition and dietary habits in esophageal cancer. PMID:23795778

Palladino-Davis, A G; Mendez, B M; Fisichella, P M; Davis, C S

2015-01-01

198

The set of habitable planets and astrobiological regulation mechanisms  

NASA Astrophysics Data System (ADS)

The number of habitable planets in the Milky Way and its temporal variation are major unknowns in the nascent fields of astrobiology and Search for ExtraTerrestrial Intelligence studies. All numerical models developed thus far have suffered from large uncertainties in the input data, in addition to our lack of understanding of the processes of astrobiological dynamics. Here, we argue that at least the input data can now be specified with more confidence, and use a simple Monte Carlo model of the Galactic Habitable Zone (GHZ) as a flexible platform for their elucidation. Previous papers have described some of the major results of this class of models; in this paper we present its mechanics and input parameters, notably the number of the habitable planets in the GHZ and their temporal distribution, based on the results of Lineweaver et al. (Lineweaver, C.H., Fenner, Y. & Gibson, B.K. (2004). Science 303, 59-62.) Regulation mechanisms (such as gamma-ray bursts or supernovae) and their temporal evolution, assumed to be main agents responsible for large-scale correlation effects, are modelled as type ? (which can sterilize part of or the entire GHZ) and type ? (which are of local importance) events with decreasing mean temporal frequency over the cosmological timescale. The considered global risk function implies as an upper limit that about one out of a hundred habitable sites will achieve high astrobiological complexity. The preliminary results of numerical modelling presented here and elsewhere imply that the lack of a sudden change from an essentially dead Galaxy to a Galaxy filled with complex life - the astrobiological phase transition - in our past (a version of Fermi's paradox) may be understood as a consequence of global astrobiological disequilibrium, strongly indicating such a transitional epoch in our future.

Vukoti?, Branislav

2010-04-01

199

Make peak flow a habit!  

MedlinePLUS

... peak flow at home with a small, plastic meter. Some peak flow meters have tabs on the side that you can ... action plan zones (green, yellow, red). If your meter does not have these, you can mark them ...

200

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

201

The Online Reading Habits of Malaysian Students  

ERIC Educational Resources Information Center

The purpose of this study is to ascertain the differences in online reading habits between genders and investigate the relationship between socio-economic status and online reading habits. Using a questionnaire, a quantitative approach was administered to 240 Form-Four students from four secondary schools in Penang Island, Malaysia. Findings…

Abidin, Mohammad Jafre Bin Zainol; Pourmohammadi, Majid; Varasingam, Nalini A/P; Lean, Ooi Choon

2014-01-01

202

Hierarchy of stroking habits at the typewriter  

Microsoft Academic Search

Studied the typing stroking habits of 82 high school students, 103 college undergraduates, and 5 faculty members and secretaries at skill levels ranging between 10 and 114 words\\/min (wpm) in order to identify the habits that account for skill and locate the skill levels at which significant changes in stroking occur. Ss typed (using 3-min timings) a series of materials

Leonard J. West; Yitzchak Sabban

1982-01-01

203

Radiological Habits Survey: Cumbrian coast beach occupancy,  

E-print Network

Radiological Habits Survey: Cumbrian coast beach occupancy, 2009 2010 Cefas contract report C3635 Environment Report RL 01/10 #12;1 Environment Report RL 01/10 Radiological Habits Survey: Cumbrian coast beach. Survey area 9 Map 1 The Cumbrian coast beach occupancy survey area 10 3.1 General observations 11 3

204

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

205

Habits of Study and Test Performance  

Microsoft Academic Search

A study habits inventory was administered to ninth- and tenth-grade students. The data were factor-analyzed to yield three constituents of study practices: distractibility, compulsiveness, and inquisitiveness. These factors satisfactorily replicated factors found in previous research and accounted for over 50% of the total variation of the items in the inventory. Tests of hypothesized relationships between habits of study and test

Thomas H. Estes; Herbert C. Richards

1985-01-01

206

Cosmological Aspects of Habitability of Exoplanets  

NASA Astrophysics Data System (ADS)

Habitable zone (HZ) defines the region around a start within which planets may support liquid water at their surfaces, which is supposed to be the necessary factor for origination and development of life on the planet. Currently we know about 30 planets inside HZ. The most interesting question is that of possibility of existence of complex life on the planets. As several space-based project aimed at searching of traces of life at exoplanets are presently being worked out, the problem of elaboration of criteria for selection out of the list of planets inside HZ those which most probably host life acquires supreme importance. It is usually implicitly assumed that planets inside HZ may host life, not taking into consideration such an important factor as the planet age. On the other hand the crucial importance of the factor meets the eye immediately. In fact, if we consider a life similar to that on the Earth, it is obvious, that planets younger than 1 Gyr can hardly bear even primitive life-forms because life needs time to originate and develop. Moreover, as a part of biochemical and metabolic processes are endothermic, and, therefore, threshold, the process of life origination may prove extremely sensitive even to tiny HZ parameter variations. Still a most of the discovered planets are known to orbit young stars (stellar population I), no older than several mullions of years. So a considerable number of planets sure HZ inhabitants may prove too young to be really inhabitable. On the other hand, 12-13 Gyr old planetary systems (population II) may happen to be more probable bearers of life. In spite of the fact that such systems are, in the average more distant from us that the population I stars, estimations of possibility of direct detection of traces of metabolism on those systems are quite optimistic, if we bear in mind planetary systems of old law-mass K-stars.

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

2014-10-01

207

Trace Element Condensation in Circumstellar Envelopes of Carbon Stars  

NASA Astrophysics Data System (ADS)

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

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

1992-07-01

208

CIRCUMSTELLAR ABSORPTION IN DOUBLE DETONATION TYPE Ia SUPERNOVAE  

SciTech Connect

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. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Guillochon, James [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Foley, Ryan J., E-mail: kenshen@astro.berkeley.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-06-20

209

STIS Imaging of the HR 4796A Circumstellar Debris Ring  

E-print Network

We have obtained high spatial resolution imaging observations of the HR 4796A circumstellar debris dust ring using the broad optical response of the Hubble Space Telescope Imaging Spectrograph in coronagraphic mode. We use our visual wavelength observations to improve upon the earlier measured geometrical parameters of the ring-like disk. Two significant flux density asymmetries are noted: (1) preferential forward scattering by the disk grains and (2) an azimuthal surface brightness anisotropy about the morphological minor axis of the disk with corresponding differential ansal brightness. We find the debris ring offset from the location of the star by ~1.4 AU, a shift insufficient to explain the differing brightnesses of the NE and SW ansae simply by the 1/$r^2$ dimmunition of starlight. The STIS data also better quantify the radial confinement of the starlight-scattering circumstellar debris, to a characteristic region debris, possibly including ices reddened by radiation exposure to the central star.

G. Schneider; A. J. Weinberger; E. E. Becklin; J. H. Debes; B. A. Smith

2008-10-01

210

The chemistry of molecular anions in circumstellar sources  

NASA Astrophysics Data System (ADS)

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

Agúndez, Marcelino; Cernicharo, José; Guélin, Michel

2015-01-01

211

The interaction of Type Ia supernovae with their circumstellar medium  

NASA Astrophysics Data System (ADS)

This PhD thesis focusses on the study of Type Ia (or thermonuclear) supernovae and their interaction with the circumstellar medium, mostly in the supernova remnant phase, but also in the first months after the explosion. The thesis consists of five chapters: 1: Introduction; 2: The imprint of a symbiotic binary progenitor on the properties of Kepler's supernova remnant; 3: Modeling the interaction of thermonuclear supernova remnants with circumstellar structures: The case of Tycho's supernova remnant; 4: The many sides of RCW 86: a type Ia supernova remnant evolving in its progenitor's wind bubble; 5: Early X-ray emission from Type Ia supernovae originating from symbiotic progenitors or recurrent novae. The individual chapter 2-5 have been or will be published in the refereed literature.

Chiotellis, Alexandros

2013-12-01

212

A Submillimeter View of Circumstellar Dust Disks in $?$ Ophiuchus  

E-print Network

We present new multiwavelength submillimeter continuum measurements of the circumstellar dust around 48 young stars in the $\\rho$ Ophiuchus dark clouds. Supplemented with previous 1.3 mm observations of an additional 99 objects from the literature, the statistical distributions of disk masses and submillimeter colors are calculated and compared to those in the Taurus-Auriga region. These basic submillimeter properties of young stellar objects in both environments are shown to be essentially identical. As with their Taurus counterparts, the $\\rho$ Oph circumstellar dust properties are shown to evolve along an empirical evolution sequence based on the infrared spectral energy distribution. The combined $\\rho$ Oph and Taurus Class II samples (173 sources) are used to set benchmark values for basic outer disk characteristics: M_disk ~ 0.005 solar masses, M_disk/M_star ~ 1%, and $\\alpha$ ~ 2 (where $F_{\

Sean M. Andrews; Jonathan P. Williams

2007-08-30

213

Habitability from a microbial point of view  

NASA Astrophysics Data System (ADS)

We examine here the definition of habitability from the point of view of primitive, anaerobic microorganisms noting that the conditions of habitability are different for the appearance of life, for established life, and for life in dormant mode [1]. Habitability in this sense is clearly distinguished from the 'prebiotic world' that precedes the appearance of life. The differences in the conditions of habitability necessary for life to appear, for life to flourish and for dormant life entrain differences in spatial and temporal scales of habitability. For the origin of life, the ingredients carbon molecules, water, nutrients and energy need to be present on time scales applicable for the origin of life (105 to a few 106 y ?), necessitating the spatial scales of a minimum of ~100 km. Established life can take advantage of short-lived habitats (hours, days) to much longer lived ones on spatial scales of 100s ?m to cm-m, whereas dormant life can survive (but not metabolise) in extreme environments for very long periods (perhaps up to millions of years) at microbial spatial scales (100s ?m - mms). Thus, it is not necessary for the whole of a planet of satellite to be habitable. But the degree of continued habitability will have a strong influence on the possibility of organisms to evolve. For a planet such as Mars, for instance, microbial habitability was (perhaps still is) at different times and in different places. Habitable conditions conducive to the appearance of life, established life and possibly even dormant life could co-exist at different locations. Reference: [1] F. Westall, D. Loizeau, F. Foucher, N. Bost, M. Bertrand, J. Vago, & G. Kminek, Astrobiology 13:9, 887-897 (2013).

Westall, Frances; Loizeau, Damien; Foucher, Frédéric; Bost, Nicolas; Bertrand, Marylène; Vago, Jorge; Kminek, Gerhard

2014-05-01

214

Variability of radiation from circumstellar grains surrounding R Coronae Borealis.  

NASA Technical Reports Server (NTRS)

Radiation at IR wavelengths from circumstellar grains surrounding R CrB has been observed for approximately three years. Variations of flux with time have been larger at a wavelength of 3.5 microns than at 11 microns. Observations at IR and visual wavelengths of R CrB are presented in a graph. Another graph shows the change in the shape of the excess radiaton between two observations spaced by a period of about one year.

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

1971-01-01

215

Observations of Circumstellar Thermochemical Equilibrium: The Case of Phosphorus  

NASA Technical Reports Server (NTRS)

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

Milam, Stefanie N.; Charnley, Steven B.

2011-01-01

216

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.

217

Circumstellar Environments of Southern M Dwarfs in the Solar Neighborhood  

NASA Astrophysics Data System (ADS)

We present the first results from SIRENS, the Search for InfraRed Excesses around Nearby Stars. Our goal is to characterize the circumstellar environments of the most common and closest stars in the Universe, the ubiquitous red dwarfs. In this phase of the study, we search 1404 southern M dwarfs within 25 parsecs of the Sun, as reported in Winters et. al 2014, using (Johnson-Kron-Cousins) optical, (2MASS) near-infrared, and (WISE) mid-infrared photometry for circumstellar disks and low-mass companions. Several studies have recently used WISE photometry to detect circumstellar disks and companions --- searches around members of the nearby young moving groups, objects with parallaxes from Hipparcos, and many northern M stars in the SDSS. However, no work has yet been done that focuses on the nearest red dwarfs, which account for at least 75% of all stars. This study, a volume-limited search around M dwarfs in the southern sky, includes statistical conclusions applicable to a majority of the stars in the universe, and opens potential gateways to a better understanding of star and planet formation.

Silverstein, Michele L.; Henry, Todd J.; Jao, Wei-Chun; Winters, Jennifer G.; Recons Team

2015-01-01

218

Additional constraints on circumstellar disks in the Trapezium Cluster  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

219

AGB/PPN/PN circumstellar rings vs. spiral  

NASA Astrophysics Data System (ADS)

With the advent of high-resolution high-sensitivity observations, spiral patterns have been revealed around several asymptotic giant branch (AGB) stars. Such patterns can provide possible evidence for the existence of central binary stars embedded in outflowing circumstellar envelopes. It is, however, not generally recognized that the binary-induced pattern, vertically extended from the orbital plane, exhibits a ring-like pattern with an inclined viewing angle. I will first review the binary-induced spiral-shell patterns on the AGB circumstellar envelopes with the effect of inclination angle with respect to the orbital plane, of which large inclination cases reveal incomplete ring-like patterns. I will describe a method of extracting such spiral-shell from the gas kinematics of an incomplete ring-like pattern to place constraints on the characteristics of the (unknown) central binary stars. This first success may open the possibility of connecting the ring-like patterns commonly found in the AGB circumstellar envelopes and in the outer parts of (pre-)planetary nebulae and pointing to the conceivable presence of central binary systems, which may give a clue for the onset of asymmetrical planetary nebulae.

Kim, H.; Taam, R. E.; Liu, S.-Y.; Hsieh, I.-T.

2014-04-01

220

Habitability design elements for a space station  

NASA Technical Reports Server (NTRS)

Habitability in space refers to the components, characteristics, conditions, and design parameters that go beyond but include the basic life sustaining requirements. Elements of habitability covered include internal environment, architecture, mobility and restraint, food, clothing, personal hygiene, housekeeping, communications, and crew activities. All elements are interrelated and need to be treated as an overall discipline. Designing for a space station is similar to designing on earth but with 'space rules' instead of ground rules. It is concluded that some habitability problems require behavioral science solutions.

Dalton, M. C.

1983-01-01

221

Diapering habits: a global perspective.  

PubMed

There are tremendous variations in diapering practices, reflecting varying cultural practices and regional difference. Around the world, more than 134 million babies are born each year, a rate of 255 births per minute or 4.3 births each second. While global population growth has been steadily declining from its peak in 1963, several regions, including the Middle East and Sub-Saharan Africa, continue to maintain high birth rates. Though the essential needs of infants are largely similar, family habits and practices during early years of life vary dramatically. This article surveys data documenting variations in diaper frequency, types, and duration of use internationally, including age of toilet training. These factors may influence diaper rash and skin health of infants and young children. Much of this data was collected as part of analysis of the international commercial diaper market, evaluated and organized as part of an international initiative on Global Infant Skin Care, and presented to a panel of experts for critique and commentary in a symposium held in December, 2013. PMID:25403934

Thaman, Lauren A; Eichenfield, Lawrence F

2014-11-01

222

Molecular content of the circumstellar disk in AB Aur: First detection of SO in a circumstellar disk  

E-print Network

Very few molecular species have been detected in circumstellar disks surrounding young stellar objects. We are carrying out an observational study of the chemistry of circumstellar disks surrounding T Tauri and Herbig Ae stars. First results of this study are presented in this note. We used the EMIR receivers recently installed at the IRAM 30m telescope to carry a sensitive search for molecular lines in the disks surrounding AB Aur, DM Tau, and LkCa 15. We detected lines of the molecules HCO+, CN, H2CO, SO, CS, and HCN toward AB Aur. In addition, we tentatively detected DCO+ and H2S lines. The line profiles suggest that the CN, HCN, H2CO, CS and SO lines arise in the disk. This makes it the first detection of SO in a circumstellar disk. We have unsuccessfully searched for SO toward DM Tau and LkCa 15, and for c-C3H2 toward AB Aur, DM Tau, and LkCa 15. Our upper limits show that contrary to all the molecular species observed so far, SO is not as abundant in DM Tau as it is in AB Aur. Our results demonstrate th...

Fuente, A; Agundez, M; Berne, O; Goicoechea, J R; Alonso-Albi, T; Marcelino, N

2010-01-01

223

Morphology of Circumstellar Environment and Some Characterictics of Circumstellar Shells of Stars with the R Coronae Borealis Variability  

E-print Network

The well-known light minima of stars with the R Coronae Borealis variability are caused by the formation of an additional circumstellar dust shell, the screening shell, inside the permanent shell. Under the assumption of uniform distribution of matter in the circumstellar environment we estimated the optical thickness of the permanent gas-and-dust shell at 0.2-0.7, and its geometrical thickness is no less than 0.4 of its own radius. The wavelength dependence of extinction is close to neutral. From spectral observations of R CrB itself in the 1985 minimum we traced the transformation of the stellar linear and molecular absorption spectrum to the emission spectrum and established that the fast variation of the U-B colour index by -0.6 in the light decline was caused purely by a change of the spectrum type. The spectrum transformation causes an increase of star brightness in the U, B, and V bands by about 1.4, 0.75, and 0.75 mags, correspondingly. It is suggested that a high-velocity (>200 km/s) matter stream through the circumstellar environment is the cause of the excitation of the emissions observed during light minima when the photospheric flux is weakening.

Alexander E. Rosenbush

2001-04-20

224

Influence of Covey Habit Training on Teams  

Microsoft Academic Search

Is there a way to provide simple guidelines for team communication that could easily be adopted by individuals? In his book, The Seven Habits of Highly Effective People, Stephen Covey suggests that applying his small collection of guidelines or \\

Debra Landry Folse; Herbert E. Longenecker; Roy J. Daigle; Stephen Covey

2003-01-01

225

Investigating habits: strategies, technologies and models  

E-print Network

Understanding habits at a biological level requires a combination of behavioral observations and measures of ongoing neural activity. Theoretical frameworks as well as definitions of habitual behaviors emerging from classic ...

Smith, Kyle S.

226

S-type and P-type Habitability in Stellar Binary Systems: A Comprehensive Approach. II. Elliptical Orbits  

NASA Astrophysics Data System (ADS)

In the first paper of this series, a comprehensive approach has been provided for the study of S-type and P-type habitable regions in stellar binary systems, which was, however, restricted to circular orbits of the stellar components. Fortunately, a modest modification of the method also allows for the consideration of elliptical orbits, which of course entails a much broader range of applicability. This augmented method is presented here, and numerous applications are conveyed. In alignment with Paper I, the selected approach considers a variety of aspects, which comprise the consideration of a joint constraint including orbital stability and a habitable region for a possible system planet through the stellar radiative energy fluxes ("radiative habitable zone"; RHZ). The devised method is based on a combined formalism for the assessment of both S-type and P-type habitability; in particular, mathematical criteria are deduced for which kinds of systems S-type and P-type habitable zones are realized. If the RHZs are truncated by the additional constraint of orbital stability, the notation of ST-type and PT-type habitability applies. In comparison to the circular case, it is found that in systems of higher eccentricity, the range of the RHZs is significantly reduced. Moreover, for a considerable number of models, the orbital stability constraint also reduces the range of S-type and P-type habitability. Nonetheless, S-, P-, ST-, and PT-type habitability is identified for a considerable set of system parameters. The method as presented is utilized for BinHab, an online code available at The University of Texas at Arlington.

Cuntz, M.

2015-01-01

227

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

228

Investigating habits: strategies, technologies and models  

PubMed Central

Understanding habits at a biological level requires a combination of behavioral observations and measures of ongoing neural activity. Theoretical frameworks as well as definitions of habitual behaviors emerging from classic behavioral research have been enriched by new approaches taking account of the identification of brain regions and circuits related to habitual behavior. Together, this combination of experimental and theoretical work has provided key insights into how brain circuits underlying action-learning and action-selection are organized, and how a balance between behavioral flexibility and fixity is achieved. New methods to monitor and manipulate neural activity in real time are allowing us to have a first look “under the hood” of a habit as it is formed and expressed. Here we discuss ideas emerging from such approaches. We pay special attention to the unexpected findings that have arisen from our own experiments suggesting that habitual behaviors likely require the simultaneous activity of multiple distinct components, or operators, seen as responsible for the contrasting dynamics of neural activity in both cortico-limbic and sensorimotor circuits recorded concurrently during different stages of habit learning. The neural dynamics identified thus far do not fully meet expectations derived from traditional models of the structure of habits, and the behavioral measures of habits that we have made also are not fully aligned with these models. We explore these new clues as opportunities to refine an understanding of habits. PMID:24574988

Smith, Kyle S.; Graybiel, Ann M.

2014-01-01

229

Anthropic selection and the habitability of planets orbiting M and K dwarfs  

NASA Astrophysics Data System (ADS)

The Earth may have untypical characteristics which were necessary preconditions for the emergence of life and, ultimately, intelligent observers. This paper presents a rigorous procedure for quantifying such "anthropic selection" effects by comparing Earth's properties to those of exoplanets. The hypothesis that there is anthropic selection for stellar mass (i.e. planets orbiting stars with masses within a particular range are more favourable for the emergence of observers) is then tested. The results rule out the expected strong selection for low mass stars which would result, all else being equal, if the typical timescale for the emergence of intelligent observers is very long. This indicates that the habitable zone of small stars may be less hospitable for intelligent life than the habitable zone of solar-mass stars. Additional planetary properties can also be analyzed, using the approach introduced here, once relatively complete and unbiased statistics are made available by current and planned exoplanet characterization projects.

Waltham, Dave

2011-10-01

230

Dynamics of exoplanetary systems, links to their habitability  

NASA Astrophysics Data System (ADS)

Our knowledge of planets' orbital dynamics, which was based on Solar System studies, has been challenged by the diversity of exoplanetary systems. Around cool and ultra cool dwarfs, the influence of tides on the orbital and spin evolution of planets can strongly affect their climate and their capacity to host surface liquid water. We illustrate the role of tides and dynamics with the extreme case of planets orbiting around brown dwarfs. In multiple planet systems, the eccentricity is excited by planet-planet interactions. Planets are therefore heated up from the inside by the tidally-induced friction. This process can heat a habitable zone planet to such a level that surface liquid water cannot exist. We also talk about the newly discovered potentially habitable Earth-sized planet Kepler-186f. Given the poorly estimated age of the system, the planet could still be evolving towards synchronization and have a high obliquity or be pseudo-synchronized with a zero obliquity. These two configurations would have a different effect on the climate of this planet.

Bolmont, E.; Raymond, S. N.; Selsis, F.

2014-12-01

231

Food Habits of Young-of-the-Year Walleyes in Okobojo Bay of Lake Oahe, South Dakota  

Microsoft Academic Search

Food habits of young-of-the-year walleyes (Stizostedion vitreum) were determined in Okobojo Bay of Lake Oahe, South Dakota from June through September, 1991. Walleyes initially fed on zooplankton but soon became piscivorous. Smallmouth buffalo (Ictiobus bubalus) were initially the most important prey fish, but rainbow smelt (Osmerus mordax) became important as walleyes moved from the littoral zone of the bay to

Jeffrey J. Jackson; David W. Willis; David G. Fielder

1992-01-01

232

The number of habitable planets in the Milky Way over cosmological time scales  

Microsoft Academic Search

A general modeling scheme for assessing the suitability for life on any Earth-like extrasolar planet is presented. This approach is based on an integrated Earth system analysis in order to calculate the habitable zone in main-sequence-star planetary systems. A new attempt by Lineweaver (1) to estimate the formation rate of Earth-like planets over cosmological time scales is applied to calculate

Werner von Bloh; Christine Bounama; Siegfried Franck

2002-01-01

233

A comparison of passerine foraging habits in two tidal marshes of different salinity  

Microsoft Academic Search

Foraging habits of dominant passerine species of the Savannah River National Wildlife Refuge, SC, were compared in freshwater\\u000a and brackish marshes. Temporal or spatial partitioning was evaluated using discriminant function analysis of the distribution\\u000a among feeding time, foraging height, marsh elevation zone, and plant-type habitat variables by red-winged blackbirds (Agelaius phoeniceus), boat-tailed grackles (Quiscalus major), long-billed marsh wrens (Cistothorus palustris),

Lance P. Peterson; George W. Tanner; Wiley M. Kitchens

1995-01-01

234

Cepheids at high angular resolution: circumstellar envelope and pulsation  

NASA Astrophysics Data System (ADS)

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

Gallenne, Alexandre

2011-12-01

235

Circumstellar Emission from Type Ib and Ic Supernovae  

E-print Network

The presumed Wolf-Rayet star progenitors of Type Ib/c supernovae have fast, low density winds and the shock waves generated by the supernova interaction with the wind are not expected to be radiative at typical times of observation. The injected energy spectrum of radio emitting electrons typically has an observed index p=3, which is suggestive of acceleration in cosmic ray dominated shocks. The early, absorbed part of the radio light curves can be attributed to synchrotron self-absorption, which leads to constraints on the magnetic field in the emitting region and on the circumstellar density. The range of circumstellar densities inferred from the radio emission is somewhat broader than that for Galactic Wolf-Rayet stars, if similar efficiencies of synchrotron emission are assumed in the extragalactic supernovae. For the observed and expected ranges of circumstellar densities to roughly overlap, a high efficiency of magnetic field production in the shocked region is required (epsilon_B ~ 0.1). For the expected densities around a Wolf-Rayet star, a nonthermal mechanism is generally required to explain the observed X-ray luminosities of Type Ib/c supernovae. Although the inverse Compton mechanism can explain the observed X-ray emission from SN 2002ap if the wind parameters are taken from the radio model, the mechanism is not promising for other supernovae unless the postshock magnetic energy density is much smaller than the electron energy density. In some cases another mechanism is definitely needed and we suggest that it is X-ray synchrotron emission in a case where the shock wave is cosmic ray dominated so that the electron energy spectrum flattens at high energy. More comprehensive X-ray observations of a Type Ib/c supernova are needed to determine whether this suggestion is correct.

Roger A. Chevalier; Claes Fransson

2006-07-10

236

A New Look at Habits and the Habit-Goal Interface  

ERIC Educational Resources Information Center

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…

Wood, Wendy; Neal, David T.

2007-01-01

237

Habitable Trinity: a new concept of a habitable environment beyond Earth  

NASA Astrophysics Data System (ADS)

Habitable Trinity, which is a newly proposed concept of a habitable environment for searching for life beyond Earth, is the coexistence of an atmosphere (consisting largely of C and N), an ocean (H and O), and a landmass (supplier of nutrients). It is the minimum requirement for the beginning of life as we know it.

Dohm, J.; Maruyama, S.

2013-09-01

238

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.

239

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

240

Further evidence for a circumstellar disk around PV Cephei  

NASA Technical Reports Server (NTRS)

Spectra of PV Cephei from 2 to 4 microns reveal a moderately strong 3 micron ice-absorption feature. Normally seen in objects with high visual obscuration, A(V) greater than 10, this absorption in an object with A(V) = 3.5-5.0 suggests the existence of a dense circumstellar disk. This paper discusses the evidence for a disk from this data and other wavelength regions, the possible origin of the 3-micron feature in PV Cephei, and the relationship between this object and other young stellar objects.

Van Citters, G. W., Jr.; Smith, R. G.

1989-01-01

241

Circumstellar Environments of MYSOs Revealed by IFU Spectroscopy  

NASA Astrophysics Data System (ADS)

Formation of massive stars (M > 8 M ?) is still not well understood and lacks of observational constraints. We observed 7 MYSO candidates using the NIFS spectrometer at Gemini North Telescope to study the accretion process at high angular resolution (~ 50 mas) and very closer to the central star. Preliminary results for 2 sources have revealed circumstellar structures traced by Brackett-Gamma, CO lines and extended H2 emission. Both sources present kinematics in the CO absorption lines, suggesting rotating structures. The next step will derive the central mass of each source by applying a keplerian model for these CO features.

Navarete, F.; Damineli, A.; Barbosa, C. L.; Blum, R. D.

2015-01-01

242

AMBER/VLTI Snapshot Survey on Circumstellar Environments  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

243

Environmental Signatures for Habitability: What to Measure and How to Rank the Habitability Potential of Mars  

NASA Technical Reports Server (NTRS)

The environmental signatures for habitability are not necessarily biosignatures, even though on Earth, they are definitive proof of habitability. It is the constant overprint of the chemical signatures of life that makes it difficult to recognize the chemical and physical properties of a potentially habitable environment as distinct from an inhabited one. Mars Science Laboratory (MSL) will soon embark on a mission to Mars to assess its past or present habitability, so it is useful to examine how we measure habitability on Earth and prepare for how that approach may differ for Mars. This exercise includes: (a) articulation of fundamental assumptions about habitability, (b) an inventory of factors that affect habitability, (c) development of metrics, measurement approach and implementation, and (d) a new classification scheme for planetary habitability that goes beyond the binary "yes" or "no." There may be dozens of factors that affect habitability and they can be weighted as a function of specific environment. However a robotic, in situ investigation even on Earth has constraints that prevent the measurement of every environmental factor, so metrics must be reduced to the most relevant subset, given available time, cost, technical feasibility and scientific importance. Many of the factors could be measured with a combination of orbital data and the MSL payload. We propose that, at a minimum, a designation of high habitability potential requires the following conditions be met: (a) thermally stable with respect to extremes and frequency of fluctuation, (b) has more than one energy source, (c) sufficient chemical diversity to make compounds with covalent and hydrogen bonding, (d) can moderate ionizing radiation enough to allow a stable or evolving pool of organic molecules, (e) must have water or other high quality polar solvent, (f) must be able to renew chemical resources (e.g., plate tectonics, volcanism or something else we haven't envisioned). A measurement approach we have taken to measure habitability on Earth is : 1. Study remote sensing data, maps, etc. 2. Decide how big an area to measure. 3. Determine the spatial sampling rate. 4. Determine the temporal sampling rate. 5. Determine the order of measurements 6. Decide where to begin measurements 7. Select locations at field site and proceed While science drives each of the steps, there are additional constraints, e.g., technical, time, cost, safety (risk). This approach is also executable on Mars. Measurement of past habitability is more challenging both for Earth and Mars where access to the past means subsurface access and confrontation with unknowns about preservation of the martian past. Some environments preserve evidence of past habitability better than others, and this is where selection of the landing site to maximize the preservation potential of habitability indicators will be key. Mars presents an opportunity to discover transitional states between habitable or not, and we offer a ranking scale for planetary habitability with Mars as the second test subject: CLASS ONE Uninhabitable and likely has never been so CLASS TWO Has a high potential but no confirmed observation of life (as defined above) CLASS THREE Inhabited (we find life) 3-A Globally inhabited 3-B Primitive life; early in its evolution, but not yet globally established 3-C Exists only in refugia -- planet heading toward class four CLASS FOUR Post-habitable (there once was life, but now it's gone) MSL provides an opportunity to carefully investigate the habitability of at least one site on Mars and it will reveal much about the possible states of planetary habitability

Conrad, Pamela G.; Eigenbrode, Jennifer L.; Mahaffy, Paul M.; Steele, Andrew

2011-01-01

244

Probing Pre-Supernova Mass Loss With Circumstellar Dust Shells  

NASA Astrophysics Data System (ADS)

Late-time (>100 day) mid-infrared (mid-IR) observations of supernovae (SNe) offer a valuable probe of the progenitor system's mass-loss. Already, this technique has been demonstrated with the Type IIn subclass, which often have large, dusty, pre-existing shells formed in pre-SN eruptions. While other SN subclasses are thought of having relatively low density circumstellar environments, a growing number of objects in other subclasses now show evidence for significant pre-SN mass loss and similar mid-IR characteristics. Long after the SN radioactive tail fades, warm dust can stay bright at mid-IR wavelengths due to alternative heating mechanisms, such as shocks. Here we propose a SNAPSHOT survey of a well-studied and high-profile SN sample, extending over a range of subclasses, including both recent and historical events with evidence of a dense CSM and/or dust. This program will (a) discover new SNe with warm dust and (b) monitor the evolution of warm dust in previously detected SNe. Harnessing the success of our previous Spitzer programs, these observations will expand upon that work by probing the similarities in and differences between the subclasses' circumstellar environments, pre-SN mass-loss, and ultimately, the progenitors themselves.

Fox, Ori; Filippenko, Alex; Skrutskie, Mike; van Dyk, Schuyler; Kelly, Pat

2014-12-01

245

Far-Infrared Water Line Emissions From Circumstellar Outflows  

E-print Network

We have modeled the far-infrared water line emission expected from circumstellar outflows from oxygen-rich late-type stars, as a function of the mass-loss rate and the terminal outflow velocity. For each mass-loss rate and terminal outflow velocity considered, we computed self-consistently the gas density, temperature, outflow velocity, and water abundance as a function of distance from the star. We then used an escape probability method to solve for the equilibrium level populations of 80 rotational states of water and thereby obtained predictions for the luminosity of a large number of far-infrared rotational transitions of water. In common with previous models, our model predicts that water will be copiously produced in the warm circumstellar gas, and that water rotational emission will dominate the radiative cooling. However, our use of a realistic radiative cooling function for water leads to a lower gas temperature than that predicted in previous models. Our predictions for the far-infrared water line luminosities are consequently significantly smaller than those obtained in previous studies. Observations to be carried out by the Infrared Space Observatory will provide a crucial test of the models presented here.

Wesley Chen; David A. Neufeld

1995-09-18

246

Extreme Carbon Overabundance in the 49 Ceti Circumstellar Gas  

NASA Astrophysics Data System (ADS)

We present analysis of C and O absorption in high-resolution HST-STIS FUV spectra of the nearby A1V star 49 Ceti. This disk system is one of the few showing the dust properties of a debris disk, but harboring relatively abundant molecular gas more characteristic of a low-mass protoplanetary disk. Since the disk is nearly edge-on, the line-of-sight to the central star passes through the disk, permitting sensitive probes of the circumstellar gas with absorption spectroscopy.Our FUV spectra show many narrow circumstellar gas lines arising from several atomic species, including neutral carbon (a gas not seen in the local ISM) and neutral oxygen. We present an estimate of the total carbon column density in the line-of-sight gas and limits on the oxygen column density. Comparing the carbon abundance to a previous measurement of the line-of-sight iron abundance, we see that the carbon is extremely overabundant relative to the solar abundance. A similar overabundance is seen in the Beta Pic disk gas, where the carbon brakes other gases from being rapidly blown out by radiation pressure. The carbon in the 49 Cet gas may play a similar role.

Roberge, Aki; Welsh, Barry; Kamp, Inga; Weinberger, Alycia J.; Grady, Carol A.

2015-01-01

247

Infrared Spectroscopy of U Equulei's Warm Circumstellar Gas  

E-print Network

Medium and high resolution spectroscopy of U Equulei from 1 to 4 microns during 1997-2003 has revealed information about its unusual circumstellar envelope, observed previously at optical and radio wavelengths. Strong absorption bands of H2O and of CO dominate the 1-4um spectrum. The gas has a mean temperature of 600 K and 12C/13C =< 10. The CO 2-0 line profiles and velocities imply no net ejection or infall and indicate either rapid radial gas motions being seen along a narrow continuum beam, or absorption by orbiting gas that is nearly coincident with a highly extended continuum source. The gas could be located in a disk-like structure. The observed high column densities of warm CO and H2 normally would be associated with sufficient dust to completely obscure the star at optical wavelengths. The observations thus indicate either a highly abnormal gas-to-dust ratio, consistent with the earlier optical observation of abundant refractory metal oxides in the circumstellar gas, or peculiar geometry and/or illumination.

T. R. Geballe; C. Barnbaum; Keith S. Noll; M. Morris

2005-02-08

248

THE PROGENITOR OF SN 2011ja: CLUES FROM CIRCUMSTELLAR INTERACTION  

SciTech Connect

Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II plateau (IIP) supernovae. The ejecta from these explosions shocks the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray parts of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work, we use X-rays observations from the Chandra and radio observations from the Australia Telescope Compact Array to study the relative importance of processes which accelerate particles and those which amplify magnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the explosion date. Multiple Chandra observations allow us to probe the history of variable mass loss from the progenitor. The ejecta expands into a low-density bubble followed by interaction with a higher density wind from a red supergiant consistent with M{sub ZAMS} {approx}> 12 M{sub Sun }. Our results suggest that a fraction of Type IIP supernovae may interact with circumstellar media set up by non-steady winds.

Chakraborti, Sayan [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ray, Alak; Yadav, Naveen [Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Colaba, Mumbai 400 005 (India); Smith, Randall [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ryder, Stuart [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); Sutaria, Firoza [Indian Institute of Astrophysics, Koramangala, Bangalore (India); Dwarkadas, Vikram V. [Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Chandra, Poonam [Department of Physics, Royal Military College of Canada, Kingston, ON K7K 7B4 (Canada); Pooley, David [Department of Physics, Sam Houston State University, Huntsville, TX (United States); Roy, Rupak, E-mail: schakraborti@fas.harvard.edu [Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital (India)

2013-09-01

249

A circumstellar molecular gas structure associated with the massive young star Cepheus A-HW 2  

NASA Technical Reports Server (NTRS)

We report the detection via VLA-D observations of ammonia of a circumstellar high-density molecular gas structure toward the massive young star related to the object Cepheus A-HW 2, a firm candidate for the powering source of the high-velocity molecular outflow in the region. We suggest that the circumstellar molecular gas structure could be related to the circumstellar disk previously suggested from infrared, H2O, and OH maser observations. We consider as a plausible scenario that the double radio continuum source of HW 2 could represent the ionized inner part of the circumstellar disk, in the same way as proposed to explain the double radio source in L1551. The observed motions in the circumstellar molecular gas can be produced by bound motions (e.g., infall or rotation) around a central mass of about 10-20 solar masses (B0.5 V star or earlier).

Torrelles, Jose M.; Rodriguez, Luis F.; Canto, Jorge; Ho, Paul T. P.

1993-01-01

250

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

2010-01-01

251

Habitability constraints/objectives for a mars manned mission: Internal architecture considerations  

NASA Astrophysics Data System (ADS)

It is generally accepted that high quality internal environment shall strongly support crew's adaptation and acceptance to situation of long isolation and confinement. Thus, this paper is an attempt to determine to which extent the resulting stress corresponding to the anticipated duration of a trip to Mars (1 and a half years to 2 and a half years) could be decreased when internal architecture of the spacecraft is properly designed. It is assumed that artificial gravity shall be available on board the Mars spacecraft. This will of course have a strong impact on internal architecture as far as a 1-g oriented design will become mandatory, at least in certain inhabited parts of the spacecraft. The review of usual Habitability functions is performed according to the peculiarities of such an extremely long mission. A particular attention is paid to communications issues and the need for privacy. The second step of the paper addresses internal architecture issues through zoning analyses. Common, Service and Personal zones need to be adapted to the constraints associated with the extremely long duration of the mission. Furthermore, due to the nature of the mission itself (relative autonomy, communication problems, monotony) and the type of selected crew (personalities, group structure) the implementation of a ``fourth zone'', so-called ``recreational'' zone, seems to be needed. This zoning analysis is then translated into some internal architecture proposals, which are discussed and illustrated. This paper is concluded by a reflection on habitability and recommendations on volumetric requirements. Some ideas to validate proposed habitability items through simulation are also discussed.

Winisdoerffer, F.; Soulez-Larivière, C.

1992-08-01

252

A Study of Circumstellar Envelopes around Bright Carbon Stars. II. Molecular Abundances  

NASA Astrophysics Data System (ADS)

We have estimated and compared circumstellar and photospheric HCN, CN, and CS abundances for a sample of bright carbon stars. The circumstellar HCN and CS abundances roughly correlate with the photospheric ones, but the former appear to be systematically overestimated by a factor of 5-10. Although we cannot exclude the presence of a circumstellar chemistry that efficiently produces HCN and CS in the inner parts of these relatively hot circumstellar envelopes, we attribute this difference between photospheric and circumstellar abundances to errors in the circumstellar envelope model used. In particular, for the low mass-loss rate objects a systematic underestimate of the mass-loss rate may be suspected. In addition to this general trend, stars that are in some sense peculiar also show circumstellar abundances that deviate significantly from the expected. There is evidence for the presence of maser features in the HCN (J = 1-0) emission toward some of the stars. The estimated circumstellar CN abundances suggest that this species is a photodissociation product of HCN. A search for circumstellar HNC, SiS, and HC3N shows that molecular emission from species other than CO, HCN, CN, and CS is very weak in these low mass-loss rate objects. An attempt has been made to determine the chemistry in the (probably detached) envelope around R Scl. The data suggest a carbon-rich chemistry. Finally, it is shown that the circumstellar 12CO/13CO and H12CN/H13CN intensity ratios roughly correlate with the photospheric 12C/13C isotope ratios for a small number of low mass-loss rate objects, although the former ratios are systematically lower than the latter by a factor of about 2.

Olofsson, H.; Eriksson, K.; Gustafsson, B.; Carlstroem, U.

1993-07-01

253

Information systems - Issues in global habitability  

NASA Technical Reports Server (NTRS)

The present investigation is concerned with fundamental issues, related to information considerations, which arise in an interdisciplinary approach to questions of global habitability. Information system problems and issues are illustrated with the aid of an example involving biochemical cycling and biochemical productivity. The estimation of net primary production (NPP) as an important consideration in the overall global habitability issue is discussed. The NPP model requires three types of data, related to meteorological information, a land surface inventory, and the vegetation structure. Approaches for obtaining and processing these data are discussed. Attention is given to user requirements, information system requirements, workstations, network communications, hardware/software access, and data management.

Norman, S. D.; Brass, J. A.; Jones, H.; Morse, D. R.

1984-01-01

254

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

255

How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30cm Space Telescope  

NASA Astrophysics Data System (ADS)

Several mission concepts are being studied to directly image planets around nearby stars. Direct imaging enables spectroscopic detection of biomarkers such as atmospheric oxygen and methane, which would be highly suggestive of extraterrestrial life. It is commonly thought that directly imaging a potentially habitable exoplanet requires telescopes with apertures of at least 1m, costing at least $1B, and launching no earlier than the 2020s.A notable exception to this is Alpha Centauri (A and B), which is an extreme outlier among FGKM stars in terms of apparent habitable zone size. Specifically, Alpha Centauri habitable zones span about 0.5-1” in stellocentric angle, ~3x wider than around any other FGKM star. This enables a ~30cm visible light space telescope equipped with a modern high performance coronagraph or starshade to resolve the habitable zone at high contrast and directly image any potentially habitable planet that may exist in the system. Due to the extreme apparent brightness of the stars, exposure times can be as short as minutes with ideal components, or days with realistic ones. This makes it possible to do color photometry on potentially habitable planets sufficient to differentiate Venus-like, Earth-like, and Mars-like planets from each other and establish the presence of Earth-pressure atmosphere through Rayleigh scattering.The raw contrast requirements for such an instrument can be relaxed to 1e-8 if the mission spends 2 years collecting tens of thousands of images on the same target, enabling a factor of 500-1000 speckle suppression in post processing. The light leak from both stars is controllable with a special wavefront control algorithm known as Multi-Star Wavefront Control (MSWC), which independently suppresses diffraction and aberrations from both stars using independent modes on the deformable mirror (see Thomas et al. at this conference).The presentation will describe the general studies and calculations in more detail and briefly present examples of small coronagraphic mission concepts currently being developed to take advantage of this opportunity. (For more detail about one such concept, see Bendek et al. at this conference).

ACEND team; ACESat team

2015-01-01

256

How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30cm Space Telescope  

NASA Astrophysics Data System (ADS)

Several mission concepts are being studied to directly image planets around nearby stars. Direct imaging enables spectroscopic detection of biomarkers such as atmospheric oxygen and methane, which would be highly suggestive of extraterrestrial life. It is commonly thought that directly imaging a potentially habitable exoplanet requires telescopes with apertures of at least 1m, costing at least 1B, and launching no earlier than the 2020s.A notable exception to this is Alpha Centauri (A and B), which is an extreme outlier among FGKM stars in terms of apparent habitable zone size. Specifically, Alpha Centauri habitable zones span about 0.5-1' in stellocentric angle, ~3x wider than around any other FGKM star. This enables a ~30cm visible light space telescope equipped with a modern high performance coronagraph or starshade to resolve the habitable zone at high contrast and directly image any potentially habitable planet that may exist in the system. Due to the extreme apparent brightness of the stars, exposure times can be as short as minutes with ideal components, or days with realistic ones. This makes it possible to do color photometry on potentially habitable planets sufficient to differentiate Venus-like, Earth-like, and Mars-like planets from each other and establish the presence of Earth-pressure atmosphere through Rayleigh scattering.The raw contrast requirements for such an instrument can be relaxed to 1e-8 if the mission spends 2 years collecting tens of thousands of images on the same target, enabling a factor of 500-1000 speckle suppression in post processing. The light leak from both stars is controllable with a special wavefront control algorithm known as Multi-Star Wavefront Control (MSWC), which independently suppresses diffraction and aberrations from both stars using independent modes on the deformable mirror (see Thomas et al. at this conference).The presentation will describe the general studies and calculations in more detail and briefly present examples of small coronagraphic mission concepts currently being developed to take advantage of this opportunity. (For more detail about one such concept, see Bendek et al. at this conference).

Belikov, Ruslan; Acend Team, Acesat Team

2015-01-01

257

Target Selection for SETI: 1. A Catalog of Nearby Habitable Stellar Systems  

E-print Network

In preparation for the advent of the Allen Telescope Array, the SETI Institute has the need to greatly expand its former list of ~2000 targets compiled for Project Phoenix, a search for extraterrestrial technological signals. In this paper we present a catalog of stellar systems that are potentially habitable to complex life forms (including intelligent life), which comprises the largest portion of the new SETI target list. The Catalog of Nearby Habitable Systems (HabCat) was created from the Hipparcos Catalogue by examining the information on distances, stellar variability, multiplicity, kinematics and spectral classification for the 118,218 stars contained therein. We also make use of information from several other catalogs containing data for Hipparcos stars on X-ray luminosity, CaII H&K activity, rotation, spectral types, kinematics, metallicity, and Stroemgren photometry. Combined with theoretical studies on habitable zones, evolutionary tracks and third body orbital stability, these data were used to remove unsuitable stars from HabCat, leaving a residue of stars that, to the best of our current knowledge, are potentially habitable hosts for complex life. While this Catalog will no doubt need to be modified as we learn more about individual objects, the present analysis results in 17,129 Hipparcos "habstars" near the Sun (75% within 140 pc), ~2200 of which are known or suspected to be members of binary or triple star systems.

Margaret C. Turnbull; Jill C. Tarter

2002-10-31

258

HABITABILITY OF EARTH-MASS PLANETS AND MOONS IN THE KEPLER-16 SYSTEM  

SciTech Connect

We demonstrate that habitable Earth-mass planets and moons can exist in the Kepler-16 system, known to host a Saturn-mass planet around a stellar binary, by investigating their orbital stability in the standard and extended habitable zone (HZ). We find that Earth-mass planets in satellite-like (S-type) orbits are possible within the standard HZ in direct vicinity of Kepler-16b, thus constituting habitable exomoons. However, Earth-mass planets cannot exist in planetary-like (P-type) orbits around the two stellar components within the standard HZ. Yet, P-type Earth-mass planets can exist superior to the Saturnian planet in the extended HZ pertaining to considerably enhanced back-warming in the planetary atmosphere if facilitated. We briefly discuss the potential detectability of such habitable Earth-mass moons and planets positioned in satellite and planetary orbits, respectively. The range of inferior and superior P-type orbits in the HZ is between 0.657-0.71 AU and 0.95-1.02 AU, respectively.

Quarles, B.; Musielak, Z. E.; Cuntz, M., E-mail: billyq@uta.edu, E-mail: zmusielak@uta.edu, E-mail: cuntz@uta.edu [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States)

2012-05-01

259

Deep optical imaging of asymptotic giant branch circumstellar envelopes  

NASA Astrophysics Data System (ADS)

We report results of a program to image the extended circumstellar envelopes of asymptotic giant branch (AGB) stars in dust-scattered Galactic light. The goal is to characterize the shapes of the envelopes to probe the mass-loss geometry and the presence of hidden binary companions. The observations consist of deep optical imaging of 22 AGB stars with high mass loss rates: 16 with the ESO 3.6 m NTT telescope, and the remainder with other telescopes. The circumstellar envelopes are detected in 15 objects, with mass loss rates ?2 × 10-6 M? yr-1. The surface brightness of the envelopes shows a strong decrease with Galactic radius, which indicates a steep radial gradient in the interstellar radiation field. The envelopes range from circular to elliptical in shape, and we characterize them by the ellipticity (E = major/minor axis) of iso-intensity contours. We find that ~50% of the envelopes are close to circular with E ? 1.1, and others are more elliptical with ~20% with E ? 1.2. We interpret the shapes in terms of populations of single stars and binaries whose envelopes are flattened by a companion. The distribution of E is qualitatively consistent with expectations based on population synthesis models of binary AGB stars. We also find that ~50% of the sample exhibit small-scale, elongated features in the central regions. We interpret these as the escape of light from the central star through polar holes, which are also likely produced by companions. Our observations of envelope flattening and polar holes point to a hidden population of binary companions within the circumstellar envelopes of AGB stars. These companions are expected to play an important role in the transition to post-AGB stars and the formation of planetary nebulae. Based on observations made at the European Southern Observatory, Chile (programs 078.D-0102, 082.D-0338 and 0.84.D-0302) and on de-archived data obtained with the ESO Very Large Telescope and with the NASA/ESA Hubble Space Telescope.Appendix A and Figs. 5, 6 are available in electronic form at http://www.aanda.org

Mauron, N.; Huggins, P. J.; Cheung, C.-L.

2013-03-01

260

Folding Corners of the Habits of Mind  

ERIC Educational Resources Information Center

Reasoning is central to what Cuoco, Goldenberg, and Mark refer to as mathematical "habits of mind" (1996). "Reasoning is an integral part of doing mathematics. Students should enter the middle grades with the view that mathematics involves examining patterns and noting regularities, making conjectures about possible generalizations,…

Wiles, Peter

2013-01-01

261

Radiological Habits Survey: Sellafield Beach Occupancy, 2007  

E-print Network

Radiological Habits Survey: Sellafield Beach Occupancy, 2007 Environment Report RL 02/08 Customer: Sellafield Beach Occupancy, 2007 Centre for Environment, Fisheries & Aquaculture Science Lowestoft Laboratory to Seamill 12 4.2.1 Beach description 12 4.2.2 Activities 13 4.3 Seamill Lane to Coulderton and Nethertown 15

262

Student Name ____________________________ THE SEARCH FOR HABITABLE PLANETS  

E-print Network

Student Name ____________________________ A103 THE SEARCH FOR HABITABLE PLANETS LIFE technological societies of intelligent beings who ask questions about the Universe around them? Although the existence of extraterrestrial life has few practical consequences for our day-to-day lives, people can

Robeson, Scott M.

263

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

264

Twelve Habits of Successful IT Professionals  

ERIC Educational Resources Information Center

In all positions, professionals must continue to develop their skills. The higher education IT profession is no exception. However, many of these skills should be developed progressively. If IT professionals can start learning these twelve skills early in their career, they will have a good chance of turning the skills into habits--and of becoming…

Hawkins, Brian L.

2006-01-01

265

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

2009-01-01

266

FOOD HABITS OF BALD EAGLES WINTERING IN  

Microsoft Academic Search

We used pellets collected from roosts to supplement incidental foraging observations to iden- tify prey species of Bald Eagles (Haliaeetus leucocephalus) and to evaluate spatial and temporal trends in their food habits while wintering in northern Arizona between 1994-96. We analyzed 1057 pellets collected from 14 roosts, and identified five mammal and 13 bird species. American Coot (Fulica americana, N

NORTHERN ARIZONA

267

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 they…

Steinkuehler, Constance; Duncan, Sean

2008-01-01

268

Food habits of bobcats in eastern Tennessee  

Microsoft Academic Search

Food habits of bobcats (Lynx rufus) in eastern Tennessee were determined from analyzing 176 cat samples collected on the Oak Ridge National Environmental Research Park. Remains of cottontail rabbits (Sylvilagus floridanus) were the most frequently occurring food item. White-tail deer (Odocoileus virginianus) and pine vole (Microtus pinetorum) remains also were found frequently in samples. Data obtained from this study indicated

J. D. Story; W. J. Galbraith; J. T. Kitchings

1982-01-01

269

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.

270

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

271

1612 MHz OH maser emission from axisymmetric circumstellar envelopes - Miras  

NASA Technical Reports Server (NTRS)

Radiative transfer calculations are performed using a modified form of the Sobolev approximation to determine the inversion of the 1612 MHz line of OH in axisymmetric circumstellar envelopes around Miras. The mass loss is assumed to be occurring in the form of a smooth wind. Line profiles and maps are presented for three models of varying degrees of asymmetry and for various orientations of the envelopes. It is concluded that the axisymmetric models can reproduce many of the features of observed profiles and maps which both the standard, spherically symmetric model and the discrete emission model cannot easily explain. The model profiles reproduce all of the general features seen in the line profiles of real sources.

Collison, Alan J.; Fix, John D.

1992-01-01

272

The Be star Achernar and its circumstellar environment  

NASA Astrophysics Data System (ADS)

The circumstellar disks ejected by many rapidly rotating B stars (so-called Be stars) offer the rare opportunity to study the structure and dynamics of gaseous disks at high spectral as well as angular resolution. Recent works, largely based on optical long baseline interferometry, showed that Achernar (? Eridani, HD10144), the brightest (V=0.46 mag) and nearest (distance of 42.75 pc) Be star is a key target to a deeper understanding of the physics of Be stars, because it displays most of features that characterizes the Be phenomenon: (i) Strong rotational rate; (ii) Residual disk; (iii) Episodic mass ejections; (iv) Quasi-cyclic disk formation/dissipation; (v) Polar wind; and (vi) Binarity.

Faes, D. M.; Carciofi, A. C.; Domiciano de Souza, A.

2014-10-01

273

The photochemistry of carbon-rich circumstellar shells  

NASA Technical Reports Server (NTRS)

The effect of ambient ultraviolet photons on the chemical structure of carbon-rich, circumstellar envelopes is investigated with a simple formulation of the time-dependent, photochemical rate equations valid for optically thick shells. Molecules injected into the shielded inner envelope are broken down when they reach the outer regions where ambient ultraviolet photons can penetrate. A quantitative description of the abundance variations is obtained for the case of uniform expansion by detailed consideration of the shielding of the radiation by the dust and molecules of the envelope. Representative results are presented to illustrate the role of shielding in defining the extent of molecular envelopes, the formation of C I and C II shells by photodestruction of carbon-bearing molecules, and the development of layered chemical structures from the photobreakup of polyatomic molecules. Photochemistry makes the outer parts of thick, carbon-rich envelopes into complex regions containing radicals, ions, and atoms which are of considerable observational and theoretical interest.

Huggins, P. J.; Glassgold, A. E.

1982-01-01

274

Molecular ions in the circumstellar envelope of IRC + 10216  

NASA Technical Reports Server (NTRS)

Assuming a steady and spherically symmetric mass loss, the spatial distribution of the ionization in a C-rich circumstellar envelope (CSE) is calculated, and it is shown that molecular ions dominate the ionization and chemistry of a large part of the CSE. Cosmic ray ionization of molecular hydrogen yields H3(+), and the photoionization of acetylene and neutral carbon yields C2H2(+) and C(+). In the system, the primary ions generate a series of heavier molecular ions by reactions with neutral molecules before being destroyed by dissociative recombination. The most promising candidate for mm-wavelength detection is found to be HCO(+), and IRC + 10216 antenna temperatures are calculated for different telescope sizes. Photoproduced C2H2(+), the most abundant intermediate distance CSE ion, may be responsible for the synthesis of various heavy hydrocarbon molecules at levels observed in IRC + 10216.

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

1986-01-01

275

An interferometric view on binarity and circumstellar envelopes of Cepheids  

NASA Astrophysics Data System (ADS)

Optical interferometry is the only technique giving access to milli-arcsecond (mas) resolution at infrared wavelengths. For Cepheids, this is a powerful and unique tool to detect the orbiting companions and the circumstellar envelopes (CSE). CSEs are interesting because they might be used to trace the Cepheid evolution history, and more particularly they could impact the distance scale. Cepheids belonging to binary systems offer an unique opportunity to make progress in resolving the Cepheid mass discrepancy. The combination of spectroscopic and interferometric measurements will allow us to derive the orbital elements, distances, and dynamical masses. Here we focus on recent results using 2- to 6-telescopes beam combiners for the Cepheids X Sgr, T Mon and V1334 Cyg.

Gallenne, A.; Kervella, P.; Mérand, A.; Monnier, J. D.; Breitfleder, J.; Pietrzy?ski, G.; Gieren, W.

2014-02-01

276

Submillimeter studies of circumstellar disks in Taurus and Orion  

E-print Network

We highlight two recent studies of circumstellar disks in the Taurus and Orion star forming regions. Using the JCMT and CSO, we measure disk fluxes in Taurus over a wide range of submillimeter wavelengths and determine the frequency dependence of the dust opacity. We find clear evidence for a systematic change in its behavior with time, most readily explained by grain growth. Using the SMA, we observed the protoplanetary disks (proplyds) in the Orion Trapezium cluster. The combination of high resolution, high frequency, and high sensitivity that this instrument provides made it possible to resolve disks from one another, distinguish their emission from background cloud material and surrounding ionized gas, and to detect thermal dust emission. This allowed us to make the first mass measurements of the proplyds and to assess their viability for planet formation.

Jonathan P. Williams; Sean M. Andrews

2005-11-19

277

Narrow circumstellar emission lines in SN 1987A  

NASA Technical Reports Server (NTRS)

Low and high dispersion short wavelength prime (SWP) spectra of SN 1987A show that the supernova's progenitor was in a post red giant branch stage of evolution at the time of its demise in February 1987. The development of narrow high temperature emission lines of N 5, N 4, N 3, C 3, He 2 and O 3 were followed since May 1987. Observations through April 1990 are presented. The lines are interpreted as arising in a low density gas surrounding the supernova which was photoionized by the extreme UV pulse at shock breakout. In this picture, their temporal evolution is determined primarily by light travel time effects and recombination. Comparison of models of circumstellar environment with the International Ultraviolet Explorer (IUE) observations are discussed.

Sonneborn, George; Cassatella, Angelo; Wamsteker, Willem; Fransson, Claes; Kirshner, Robert; Gilmozzi, Roberto; Panagia, Nino

1990-01-01

278

The Circumstellar Disk of HD 141569 Imaged with NICMOS.  

PubMed

Coronagraphic imaging with the Near-Infrared Camera and Multiobject Spectrometer on the Hubble Space Telescope reveals a large, approximately 400 AU (4&arcsec;) radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected light image at 1.1 µm shows the disk oriented at a position angle of 356&j0;+/-5&j0; and inclined to our line of sight by 51&j0;+/-3&j0;; the intrinsic scattering function of the dust in the disk makes the side inclined toward us, the eastern side, brighter. The disk flux density peaks 185 AU (1&farcs;85) from the star and falls off to both larger and smaller radii. A region of depleted material, or a gap, in the disk is centered 250 AU from the star. The dynamical effect of one or more planets may be necessary to explain this morphology. PMID:10511512

Weinberger; Becklin; Schneider; Smith; Lowrance; Silverstone; Zuckerman; Terrile

1999-11-01

279

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 author…

Oshikanlu, Seyi

2006-01-01

280

Radiological Habits Survey: Environment Report RL 03/13  

E-print Network

Radiological Habits Survey: 2013 Environment Report RL 03/13 Cefas contract report C2848 Radiological Habits Survey: Springfields, 2012 V.E. Ly, F.J. Clyne, C.J. Garrod and A. Dewar Peer reviewed by G.E., Clyne, F.J., Garrod, C.J. and Dewar, A., 2013. Radiological Habits Survey: Springfields, 2012. RL 03

281

Radiological Habits Survey: Barrow and the south-west  

E-print Network

Radiological Habits Survey: Barrow and the south-west 2013 Environment Report RL 01/13 Cefas Report RL 01/13 Final report Radiological Habits Survey: Barrow and the south-west Cumbrian coast, 2012 C.E., Rumney, P. and Papworth, G.P., 2013. Radiological Habits Survey: Barrow and the south-west Cumbrian coast

282

Radiological Habits Survey: Environment Report RL 02a/13  

E-print Network

Radiological Habits Survey: 2013 Environment Report RL 02a/13 Cefas contract report C2848 Low Level Final report Radiological Habits Survey: Low Level Waste Repository, 2012 F.J. Clyne, C.J. Garrod, V. and Papworth, G.P., 2013. Radiological Habits Survey: Low Level Waste Repository, 2012. RL 02a/13. Cefas

283

Radiological Habits Survey: Environment Report RL 03/12  

E-print Network

Radiological Habits Survey: 2012 Environment Report RL 03/12 Cefas contract report C2848/12 Final report Radiological Habits Survey: Aldermaston and Burghfield, 2011 V.E. Ly, C.J. Garrod, F should be cited as: Ly, V.E., Garrod, C.J., Clyne, F.J. and Rumney, P., 2012. Radiological Habits Survey

284

Beta Pic-like Circumstellar Gas Disk Around 2 And  

NASA Technical Reports Server (NTRS)

This grant was awarded to support the data analysis and publication of results from our project entitled P Pic-like Circumstellar Gas Disk Around 2 And . We proposed to obtain FUSE observations of 2 And and study the characteristics and origin of its circumstellar gas. We observed 2 Andromedae with FUSE on 3-4 July 2001 in 11 exposures with a total exposure time of 21,289 seconds through the LWRS aperture. Our data were calibrated with Version 1.8.7 of the CALFUSE pipeline processing software. We corrected the wavelength scale for the heliocentric velocity error in this version of the CALFUSE software. The relative accuracy of the calibrated wavelength scale is +/- 9 km/s . We produced a co-added spectrum in the LiF 1B and LiF 2A channels (covering the 1100 to 1180 A region) by cross-correlating the 11 individual exposures and doing an exposure-time weighted average flux. The final co-added spectra have a signal-to-noise ratio in the stellar continuum near 1150 A of about 20. To obtain an absolute wavelength calibration, we cross-correlated our observed spectra with a model spectrum to obtain the best fit for the photospheric C I lines. Because the photospheric lines are very broad, this yields an absolute accuracy for the wavelength scale of approx.+/- 15 km/s. We then rebinned 5 original pixels to yield the optimal sampling of .033 A for each new pixel, because the calibrated spectra oversample the spectral resolution for FUSE+LWRS (R = 20,000 +/- 2,000).

Cheng, Patricia

2003-01-01

285

Circumstellar Dust Disks around Stars with Known Planetary Companions  

NASA Astrophysics Data System (ADS)

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 system's Kuiper Belt. To date, we have detected circumstellar disks around three such stars: 55 Cnc, ? CrB, and HD 210277. All these systems now resemble mature planetary systems with Jupiter-mass companions and Kuiper Belt-like disks. Our previous detection of the 55 Cnc disk (Trilling & Brown) is included here to place that disk in the context of the other two newly detected disks. Measuring the inclinations of the disks and assuming the disks are coplanar with the planets' orbits determines the masses of the planets around these three stars to be 1.9+1.1-0.4 MJ, 1.5+0.2-0.1 MJ, and 2.2+0.6-0.2 MJ, respectively (1 MJ is one Jupiter mass). We also report nondetections for three stars--51 Peg, ? And, and Gl876--that are known to have radial velocity companions. A number of possibilities exist to explain nondetections of disks, from the absence of a disk to limits on disk mass, radial extent, or inclination. We may also be looking through a disk's central hole, especially for the nearby star Gl876. The radial brightness profiles of each of the observed disks follow a power law with index ~-5, including a power of -2 from the stellar flux drop off, similar to the suggested value for our solar system's Kuiper Belt. This likely suggests that uniform physical processes govern the Kuiper Belt's population out to at least 100 AU, and may be ubiquitous among disks. Last, we discuss how disk characterizations can lead us toward refining theories of planetary system formation.

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

2000-01-01

286

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

287

Stellar orbit evolution in close circumstellar disc encounters  

NASA Astrophysics Data System (ADS)

The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3D, focusing on disc-disc interactions that result from stellar flybys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericentre separation rp, disc orientation and disc-star mass ratio (Md/M*) on the orbital evolution of the host stars. Close encounters (2rp ? disc radius) can truncate discs on very short time-scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that for realistic primordial disc masses Md ? 0.1M*, non-colliding encounters induce minor orbital changes, which is consistent with analytic calculations of encounters in the linear regime. The same disc masses produce entirely different results for grazing/colliding encounters. In the latter case, rapidly cooling discs lose orbital energy by radiating away the energy excess of the shock-heated gas, thus causing capture of the host stars into a bound orbit. In rare cases, a tight binary with a circumbinary disc forms as a result of this encounter.

Muñoz, D. J.; Kratter, K.; Vogelsberger, M.; Hernquist, L.; Springel, V.

2015-01-01

288

Factors Impacting Habitable Volume Requirements: Results from the 2011 Habitable Volume Workshop  

NASA Technical Reports Server (NTRS)

This report documents the results of the Habitable Volume Workshop held April 18-21, 2011 in Houston, TX at the Center for Advanced Space Studies-Universities Space Research Association. The workshop was convened by NASA to examine the factors that feed into understanding minimum habitable volume requirements for long duration space missions. While there have been confinement studies and analogs that have provided the basis for the guidance found in current habitability standards, determining the adequacy of the volume for future long duration exploration missions is a more complicated endeavor. It was determined that an improved understanding of the relationship between behavioral and psychosocial stressors, available habitable and net habitable volume, and interior layouts was needed to judge the adequacy of long duration habitat designs. The workshop brought together a multi-disciplinary group of experts from the medical and behavioral sciences, spaceflight, human habitability disciplines and design professionals. These subject matter experts identified the most salient design-related stressors anticipated for a long duration exploration mission. The selected stressors were based on scientific evidence, as well as personal experiences from spaceflight and analogs. They were organized into eight major categories: allocation of space; workspace; general and individual control of environment; sensory deprivation; social monotony; crew composition; physical and medical issues; and contingency readiness. Mitigation strategies for the identified stressors and their subsequent impact to habitat design were identified. Recommendations for future research to address the stressors and mitigating design impacts are presented.

Simon, M.; Whitmire, A.; Otto, C.; Neubek, D. (Editor)

2011-01-01

289

Formation, Tidal Evolution, and Habitability of the Kepler-186 System  

NASA Astrophysics Data System (ADS)

The Kepler-186 system consists of five planets orbiting an early M dwarf. The planets have physical radii of 1.0-1.50 R ? and orbital periods of 4-130 days. The 1.1 R ? Kepler-186f with a period of 130 days is of particular interest. Its insolation of roughly 0.32 S ? places it within the surface liquid water habitable zone (HZ). We present a multifaceted study of the Kepler-186 system, using two sets of parameters which are consistent with the data and also self-consistent. First, we show that the distribution of planet masses can be roughly reproduced if the planets were accreted from a high surface density disk presumably sculpted by an earlier phase of migration. However, our simulations predict the existence of one to two undetected planets between planets e and f. Next, we present a dynamical analysis of the system including the effect of tides. The timescale for tidal evolution is short enough that the four inner planets must have small obliquities and near-synchronous rotation rates. The tidal evolution of Kepler-186f is slow enough that its current spin state depends on a combination of its initial spin state, its dissipation rate, and the stellar age. Finally, we study the habitability of Kepler-186f with a one-dimensional climate model. The planet's surface temperature can be raised above 273 K with 0.5-5 bars of CO2, depending on the amount of N2 present. Kepler-186f represents a case study of an Earth-sized planet in the cooler regions of the HZ of a cool star.

Bolmont, Emeline; Raymond, Sean N.; von Paris, Philip; Selsis, Franck; Hersant, Franck; Quintana, Elisa V.; Barclay, Thomas

2014-09-01

290

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E-print Network

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Kainen, Paul C.

291

Detection of O2 Produced Abiotically on Habitable but Lifeless Planets around M-dwarfs  

NASA Astrophysics Data System (ADS)

High atmospheric abundances of oxygen has been widely considered to be a reliable biosignature for life on exoplanets in the habitable zones of all types of stars. Recently it was proposed that the unique UV spectra of observed planet-hosting M dwarfs could lead to the buildup of molecular oxygen in the atmospheres of habitable but lifeless planets around these stars (Tian et al. 2014). However, the detectability of the accumulated O2 was not modeled. In this work we developed a new line by line radiative transfer model based on HITRAN database and used the model to simulate the reflectivity in the visible and near IR range. We show that abiotically produced and maintained O2 in the 0.2% level is observable at 13105 cm-1 (0.76 ?m) with the spectra resolution of 70.

Li, Tong; Tian, Feng

2014-04-01

292

Applying behavior analysis to clinical problems: review and analysis of habit reversal  

Microsoft Academic Search

This article provides a review and analysis of habit reversal, a multicomponent procedure developed by Azrin and Nunn (1973, 1974) for the treatment of nervous habits, tics, and stuttering. The article starts with a discussion of the behaviors treated with habit reversal, behavioral covariation among habits, and functional analysis and assessment of habits. Research on habit reversal and simplified versions

RAYMOND G. MILTENBERGER; R. WAYNE FUQUA; D W Woods

1998-01-01

293

Habitability Assessment at Gale Crater: Implications from Initial Results  

NASA Technical Reports Server (NTRS)

Mars Science Laboratory has made measurements that contribute to our assessment of habitability potential at Gale Crater. Campaign organization into a consistent set of measurable parameters allows us to rank the relative habitability potential of sites we study, ultimately laying a foundation for a global context inclusive of past and future Mars mission observations. Chemical, physical, geological and geographic attributes shape environments. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential. Metrics for habitability assessment based on field work at sites sharing features analogous to Mars have previously been suggested. Grouping these metrics helps us to develop an index for their application to habitability assessment. The index is comprised of the weighted values for four groups of parameters, the habitability threshold for each is to be determined.

Conrad, Pamela G.; Archer, D.; Atreya, S.; Blake, D.; Coll, P.; delaTorre, M.; Edgett, K.; Eigenbrode, J.; Fisk, M.; Freissent, C.; Franz, H.; Glavin, D. P.; Gomez, F.; Haberle, R.; Hamilton, V.; Jones, J.; Kah, L.; Leshin, L.; Mchaffy, P. M.; McAdam, A.; McKay, C.; Navarro-Gonzalez, R.; Steele, A.; Stern, J.; Treiman, A.

2013-01-01

294

STS mission duration enhancement study: (orbiter habitability)  

NASA Technical Reports Server (NTRS)

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 cup foot restraints. Past studies that used volumetric terms and requirements for crew size versus mission duration were reviewed and common definitions of key habitability terms were established. An accurately dimensioned drawing of the orbiter mid-deck, locating all of the known major elements was developed. Finally, it was established that orbiter duration and crew size can be increased with minimum modification and impact to the crew module. Preliminary concepts of the aft med-deck, external versions of expanded tunnel adapters (ETA), and interior concepts of ETA-3 were developed and comparison charts showing the various factors of volume, weight, duration, size, impact to orbiter, and number of sleep stations were generated.

Carlson, A. D.

1979-01-01

295

Dead Zone  

NSDL National Science Digital Library

In this video segment adapted from the independent film Big River: A King Corn Companion, the filmmakers explain how agricultural runoff from the Midwest has contributed to a massive "dead zone" in the Gulf of Mexico. A cornfield treated with conventional chemical fertilizer promises a bumper crop, but chemical runoff from the farm enters the Iowa River, eventually draining into the Mississippi River and the Gulf of Mexico. In the Gulf, these dissolved nutrients allow algae to flourish. The algae's decay depletes the water of oxygen, creating a dead zone where shrimp and fish are starved of oxygen and die. A background essay, discussion questions, and standards correlations are also provided.

2010-08-31

296

Habits of Mind for the Science Laboratory  

NSDL National Science Digital Library

Laboratory experience should be an integral part of any high school science program, especially laboratory activities designed so that students gather data, explore concepts, and answer questions through inquiry. So, how can science teachers avoid negligence and minimize the risk of accidents when preparing for, instructing, and supervising students before, during, and after lab? Cultivating the following "habits of mind" at each stage of laboratory work is the first big step toward achieving safety in the laboratory setting.

Eick, Charles; Hayes, Lisa; Smith, Margaret

2005-09-01

297

Gambling Habits Among Aged African Americans  

Microsoft Academic Search

In a cross-sectional study we investigated the correlates of gambling habits among a sample of 80 independently living African-American elderly persons. The participants were selected from two Senior Citizen Centers that provide inexpensive or free pleasure trips from Los Angeles, California to gambling sites in Nevada. The data for this study were collected through face-to-face interviews conducted by three trained

Mohsen Bazargan; Shahrzad H. Bazargan; Mahfuja Akanda

2001-01-01

298

Thermal-Orbital Coupled Tidal Heating and Habitability of Martian-sized Extrasolar Planets around M Stars  

NASA Astrophysics Data System (ADS)

M-type stars are good targets in the search for habitable extrasolar planets. Due to their low effective temperatures, the habitable zone of M stars is very close to the stars themselves. For planets that are close to their stars, tidal heating plays an important role in thermal and orbital evolutions, especially when the planet's orbit has a relatively large eccentricity. Although tidal heating interacts with the thermal state and the orbit of the planet, such coupled calculations for extrasolar planets around M stars have not been conducted. We perform coupled calculations using simple structural and orbital models and analyze the thermal state and habitability of a terrestrial planet. Considering this planet to be Martian-sized, the tide heats up and partially melts the mantle, maintaining an equilibrium state if the mass of the star is less than 0.2 times the mass of the Sun and the initial eccentricity of the orbit is more than 0.2. The reduction of heat dissipation due to the melted mantle allows the planet to stay in the habitable zone for more than 10 Gyr even though the orbital distance is small. The surface heat flux at the equilibrium state is between that of Mars and Io. The thermal state of the planet mainly depends on the initial value of the eccentricity and the mass of the star.

Shoji, D.; Kurita, K.

2014-07-01

299

The quantitative modelling of human spatial habitability  

NASA Technical Reports Server (NTRS)

A theoretical model for evaluating human spatial habitability (HuSH) in the proposed U.S. Space Station is developed. Optimizing the fitness of the space station environment for human occupancy will help reduce environmental stress due to long-term isolation and confinement in its small habitable volume. The development of tools that operationalize the behavioral bases of spatial volume for visual kinesthetic, and social logic considerations is suggested. This report further calls for systematic scientific investigations of how much real and how much perceived volume people need in order to function normally and with minimal stress in space-based settings. The theoretical model presented in this report can be applied to any size or shape interior, at any scale of consideration, for the Space Station as a whole to an individual enclosure or work station. Using as a point of departure the Isovist model developed by Dr. Michael Benedikt of the U. of Texas, the report suggests that spatial habitability can become as amenable to careful assessment as engineering and life support concerns.

Wise, James A.

1988-01-01

300

Study of television viewing habits in children.  

PubMed

Previous studies from developing countries have reported that Television (TV) viewing, if excessive and of poor quality has a proven negative influence on child health. Indian studies on this subject are few. The present study aimed at determining TV viewing habits of children and their families as well as parental perspectives on the impact of TV on child health using a provider completed indigenously developed questionnaire in Hindi. The study group comprised of 109 children attending a government hospital who belonged predominantly to lower socio-economic strata with poor maternal literacy. It was observed that 100 % children watched excessive TV (> 2 h daily), with majority viewing unsupervised and low quality content. There were minimal parental restrictions and no active discussion regarding contents. Negative impact was found on play, hobbies, sleep hygiene and eating habits in most children. Most parents were unaware of unhealthy viewing and the associated deleterious effects. As pediatricians we need to enquire about TV viewing habits routinely and educate parents about appropriate TV viewing. PMID:24682808

Mukherjee, Sharmila Banerjee; Gupta, Yogita; Aneja, Satinder

2014-11-01

301

Using Drained Spacecraft Propellant Tanks for Habitation  

NASA Technical Reports Server (NTRS)

A document proposes that future spacecraft for planetary and space exploration be designed to enable reuse of drained propellant tanks for occupancy by humans. This proposal would enable utilization of volume and mass that would otherwise be unavailable and, in some cases, discarded. Such utilization could enable reductions in cost, initial launch mass, and number of launches needed to build up a habitable outpost in orbit about, or on the surface of, a planet or moon. According to the proposal, the large propellant tanks of a spacecraft would be configured to enable crews to gain access to their interiors. The spacecraft would incorporate hatchways, between a tank and the crew volume, that would remain sealed while the tank contained propellant and could be opened after the tank was purged by venting to outer space and then refilled with air. The interior of the tank would be pre-fitted with some habitation fixtures that were compatible with the propellant environment. Electrical feed-throughs, used originally for gauging propellants, could be reused to supply electric power to equipment installed in the newly occupied space. After a small amount of work, the tank would be ready for long-term use as a habitation module.

Thomas, Andrew S. W.

2009-01-01

302

An Optical Study of the Circumstellar Environment Around the Crab Nebula  

NASA Technical Reports Server (NTRS)

Long-slit spectra of two peripheral regions around the Crab Nebula show no H(alpha) emission down to a flux level of 1.5 x 10(exp -7)erg/sq cm s sr (0.63 Rayleigh), corresponding to an emission measure limit of 4.2 cm(sup - 6) pc (3(sigma)) assuming A(sub V)= 1.6(sup m) and T(sub e)=7000 K. This is below the flux levels reported by Murdin & Clark (Nature, 294, 543 (198 1)) for an H(alpha) halo around the Crab. Narrow H(beta) emission as described by Murdin (MNRAS, 269, 89 (1994)) is detected but appears to be Galactic emission unassociated with the remnant. A review of prior searches indicates no convincing observational evidence to support either a high- or low-velocity envelope around the remnant. Spectral scans confirm a well-organized, N-S expansion asymmetry of the filaments with a approx. 500 km/s central velocity constriction as described by MacAlpine et al. (ApJ, 342, 364 (1989)) and Lawrence et (it. (AJ, 109, 2635 (1995)] but questioned by Hester et al. (ApJ, 448, 240 (1995)). The velocity pinching appears to coincide with an cast-west chain of bright [O III] and helium-rich filaments. This expansion asymmetry might be the result of ejecta interaction with a disk of circumstellar matter, but such a model may be inconsistent with H and He filament abundances in the velocity constriction zone. A re-analysis of the remnant's total mass suggests that the filaments contain 4.6 +/- 1.8 M(solar) in ionized and neutral cas, about twice that of earlier estimates. For a 10M(solar) progenitor, this suggests that approx.equals 4M(solar) remains to be detected in an extended halo or wind.

Fesen, Robert A.; Shull, J. Michael; Hurford, Alan P.

1997-01-01

303

Dust Migration and Morphology in Optically Thin Circumstellar Gas Disks  

NASA Astrophysics Data System (ADS)

We analyze the dynamics of gas-dust coupling in the presence of stellar radiation pressure in circumstellar disks, which are in a transitional stage between the gas-dominated, optically thick, primordial nebulae, and the dust-dominated, optically thin Vega-type disks. Dust grains undergo radial migration, either leaving the disk owing to a strong radiation pressure or seeking a stable equilibrium orbit in corotation with gas. In our models of A-type stars surrounded by a total gas mass from a fraction to dozens of Earth masses, the outward migration speed of dust is comparable with the gas sound speed. Equilibrium orbits are circular, with exception of those significantly affected by radiation pressure, which can be strongly elliptic with apocenters extending beyond the bulk of the gas disk. The migration of dust gives rise to radial fractionation of dust and creates a variety of possible observed disk morphologies, which we compute by considering the equilibrium between the dust production and the dust-dust collisions removing particles from their equilibrium orbits. Large grains (typically >~200 ?m) are distributed throughout most of the gas disk. Smaller grains (in the range of 10-200 ?m) concentrate in a prominent ring structure in the outer region of the gas disk (presumably at radius ~100 AU), where gas density is rapidly declining with radius. The width and density, as well as density contrast of the dust ring with respect to the inner dust disk, depend on the distribution of gas and the mechanical strength of the particles. Our results open the prospect for deducing the distribution of gas in circumstellar disks by observing their dust. We have qualitatively compared our models with two observed transitional disks around HR 4796A and HD 141569A. Dust migration can result in observation of a ring or a bimodal radial dust distribution, possibly very similar to the ones produced by gap-opening planets embedded in the disk, or shepherding it from inside or outside. We conclude that a convincing planet detection via dust imaging should include specific nonaxisymmetric structure (spiral waves, streamers, resonant arcs) following from the dynamical simulations of perturbed disks.

Takeuchi, Taku; Artymowicz, Pawel

2001-08-01

304

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

305

Enhanced Avoidance Habits in Obsessive-Compulsive Disorder  

PubMed Central

Background Obsessive-compulsive disorder (OCD) is a psychiatric condition that typically manifests in compulsive urges to perform irrational or excessive avoidance behaviors. A recent account has suggested that compulsivity in OCD might arise from excessive stimulus-response habit formation, rendering behavior insensitive to goal value. We tested if OCD patients have a bias toward habits using a novel shock avoidance task. To explore how habits, as a putative model of compulsivity, might relate to obsessions and anxiety, we recorded measures of contingency knowledge, explicit fear, and physiological arousal. Methods Twenty-five OCD patients and 25 control subjects completed a shock avoidance task designed to induce habits through overtraining, which were identified using goal-devaluation. The relationship between habitual behavior, erroneous cognitions, and physiological arousal was assessed using behavior, questionnaires, subjective report, and skin conductance responses. Results A devaluation sensitivity test revealed that both groups could inhibit unnecessary behavioral responses before overtraining. Following overtraining, OCD patients showed greater avoidance habits than control subjects. Groups did not differ in conditioned arousal (skin conductance responses) at any stage. Additionally, groups did not differ in contingency knowledge or explicit ratings of shock expectancy following the habit test. Habit responses were associated with a subjective urge to respond. Conclusions These data indicate that OCD patients have a tendency to develop excessive avoidance habits, providing support for a habit account of OCD. Future research is needed to fully characterize the causal role of physiological arousal and explicit fear in habit formation in OCD. PMID:23510580

Gillan, Claire M.; Morein-Zamir, Sharon; Urcelay, Gonzalo P.; Sule, Akeem; Voon, Valerie; Apergis-Schoute, Annemieke M.; Fineberg, Naomi A.; Sahakian, Barbara J.; Robbins, Trevor W.

2014-01-01

306

Debris Disks Around Nearby Stars with Circumstellar Gas  

E-print Network

We conducted a survey for infrared excess emission from 16 nearby main sequence shell stars using the Multiband Imaging Photometer for Spitzer (MIPS) on the Spitzer Space Telescope. Shell stars are early-type stars with narrow absorption lines in their spectra that appear to arise from circumstellar (CS) gas. Four of the 16 stars in our survey showed excess emission at 24 microns and 70 microns characteristic of cool CS dust and are likely to be edge-on debris disks. Including previously known disks, it appears that the fraction of protoplanetary and debris disks among the main sequence shell stars is at least 48% +/- 14%. While dust in debris disks has been extensively studied, relatively little is known about their gas content. In the case of Beta Pictoris, extensive observations of gaseous species have provided insights into the dynamics of the CS material and surprises about the composition of the CS gas coming from young planetesimals (e.g. Roberge et al. 2006). To understand the co-evolution of gas and ...

Roberge, Aki

2007-01-01

307

Debris Disks Around Nearby Stars with Circumstellar Gas  

E-print Network

We conducted a survey for infrared excess emission from 16 nearby main sequence shell stars using the Multiband Imaging Photometer for Spitzer (MIPS) on the Spitzer Space Telescope. Shell stars are early-type stars with narrow absorption lines in their spectra that appear to arise from circumstellar (CS) gas. Four of the 16 stars in our survey showed excess emission at 24 microns and 70 microns characteristic of cool CS dust and are likely to be edge-on debris disks. Including previously known disks, it appears that the fraction of protoplanetary and debris disks among the main sequence shell stars is at least 48% +/- 14%. While dust in debris disks has been extensively studied, relatively little is known about their gas content. In the case of Beta Pictoris, extensive observations of gaseous species have provided insights into the dynamics of the CS material and surprises about the composition of the CS gas coming from young planetesimals (e.g. Roberge et al. 2006). To understand the co-evolution of gas and dust through the terrestrial planet formation phase, we need to study the gas in additional debris disks. The new debris disk candidates from this Spitzer survey double the number of systems in which the gas can be observed right now with sensitive line of sight absorption spectroscopy.

Aki Roberge; Alycia J. Weinberger

2007-11-28

308

Molecular catastrophes and circumstellar SiO masers  

NASA Technical Reports Server (NTRS)

Understanding the complex SiO maser regions of highly evolved stars can be improved through multiwavelength studies of 'premaser' stars, such as M0-M4 giants and semiregular variables, which can be placed on normal H-R diagrams unlike most of the OH-IR stars. I argue that SiO masers are a key part of the transformation of hot stellar plasma into cold circumstellar silicate dust, in the outflows from evolved, oxygen rich stars. Evidence for this statement rests on the following: (1) red giant mass loss originates in a stochastic, amsotropic manner; (2) SiO maser maps of Miras and red supergiants show numerous maser spots within a few stellar radii; (3) molecules and dust naturally form in a cooling outflow; (4) the IRAS Low Resolution Spectrometer provided evidence for diverse and variable 10 micron silicate features in Miras, and these shapes correlate well with the proposed maser chronology, suggesting a formation and annealing sequence. The theory for the occurrence of SiO masers involving thermal instability, related 'new' physics, recent calculations and a prediction are discussed.

Stencel, Robert E.

1993-01-01

309

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

310

The formation and structure of circumstellar and interstellar dust  

NASA Technical Reports Server (NTRS)

The intriguing abundance of long linear carbon chain molecules in some dark clouds and in circumstellar shells is still not well understood. Recent laboratory studies which have probed this problem indicate that when carbon vapor nucleates to form particles, linear chains and hollow cage molecules (fullerenes) also form at more-or-less the same time. The results have consequences for the formation, structures and spectroscopic properties of the molecular and dust components ejected from cool carbon-rich stars. A most interesting result of the experimental observations relates to the probability that a third character in addition to the chains and grains, the C(sub 60) molecule probably in the form of the ion C(sub 60)(sup +) in the less shielded regions, is present and perhaps responsible for some of the ubiquitously observed interstellar spectroscopic features such as the Diffuse Interstellar Features, the 2170A UV Absorption or perhaps some of the Unidentified Infrared Bands. Further study of small carbon particles which form in the gas phase has resulted in the discovery that they have quasi-icosahedral spiral shell structures. The role that such species may play in the interstellar medium as well as that played by C(sub 60) (or C sub 60 sup +) should soon be accessible to verification by a combination of laboratory experiment and astronomical spectroscopy.

Kroto, H. W.

1990-01-01

311

The Ever Changing Circumstellar Nebula Around UW Centauri  

NASA Astrophysics Data System (ADS)

We will present new images of the unique reflection nebula surrounding the R Coronae Borealis Star, UW Cen. This nebula changes its appearance significantly on timescales of a year or less as different parts are illuminated by light from the central star modulated by shifting thick dust clouds near its surface. These dust clouds form and dissipate at irregular intervals causing the well-known declines in the R Coronae Borealis star lightcurve. In this way, the central star acts like a lighthouse shining through holes in the dust clouds and lighting up different portions of the nebula. The new images may enable us to use the light echo to calculate an accurate distance to UW Cen, investigate the morphology of the nebula in detail to study whether this object is related to planetary nebulae and the final helium shell flash stars and use the illumination of the nebula to discern the pattern of new circumstellar dust clouds. Understanding the RCB stars is a key test for any theory which aims to explain hydrogen deficiency in post-Asymptotic Giant Branch stars.

Clayton, G. C.; Beshara, Y.; Smith, T. L.; Gordon, K. D.; Kerber, F.; Lawson, W. A.; Crause, L.; Galaz, G.; Rauch, T.

2000-12-01

312

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

313

A WISE Survey of Circumstellar Disks in Taurus  

NASA Astrophysics Data System (ADS)

We have compiled photometry at 3.4, 4.6, 12, and 22 ?m from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ~M8 (M >~ 0.03 M ?). Based on data from the Wide-field Infrared Survey Explorer, the Spitzer Space Telescope, the Two Micron All-Sky Survey, the NASA Infrared Telescope Facility, the Hobby-Eberly Telescope, and the Digitized Sky Survey.

Esplin, T. L.; Luhman, K. L.; Mamajek, E. E.

2014-04-01

314

Thermal structure of circumstellar discs around A stars  

NASA Astrophysics Data System (ADS)

IRAS and ISO observations revealed that a large number of A stars is surrounded by dust discs. At least for a subgroup, the lambda Bootis stars, there is growing evidence that these are pre-main-sequence stars surrounded by gas and dust discs (Holweger & Rentzsch-Holm 1995; Holweger, Hempel & Kamp 1999). In order to understand the physical and chemical processes in such circumstellar discs, we developed thin hydrostatic equilibrium models which contain a sophisticated chemical network and account for the detailed photospheric flux of the central star (Kamp & Bertoldi 1999). In a first approximation we assumed that gas and dust have the same temperature due to strong collisional coupling, and that the temperature is determined by the radiative equilibrium of the dust. Now we present disc models where the chemical equilibrium is solved subject to the energy balance of gas and dust. We take into account a large number of heating and cooling processes in detail, like for example heating by photodissociation or formation of H_2 or cooling by C and O fine structure lines. We find that frictional heating by dust grains may be the dominant heating source depending on the drift velocity of dust grains and hence the efficiency of radiation pressure. In the absence of a large grain drift velocity gas-dust collisions determine the gas temperature for densities larger than 10^6 cm^{-3}.

Kamp, I.; Holweger, H.

315

The circumstellar gas cloud around Beta Pictoris. II  

NASA Astrophysics Data System (ADS)

An analysis of high-quality echelle spectra of Beta Pic, obtained in October 1984 and March 1985 using the 1.4 m La Silla ESO telescope, indicates that the K line of Ca II is wider than the D lines of Na I, and that a velocity difference of 2 km/s exists between the approximate centers of the lines of the two species. In the circumstellar disk around Beta Pic, it is suggested that the Na I is located in an outer region which contains nearly all of the mass of the disk, and that most of the Ca II lies in an inner region having a 2 km/s redshift with respect to the outer one. Assuming a power law distribution of the total gas density throughout the disk, the gas extends inward to a radius of about 0.4 AU, and the interior region consists of a thin annulus of gas having a solar abundance of calcium.

Vidal-Madjar, A.; Ferlet, R.; Hobbs, L. M.; Gry, C.; Albert, C. E.

1986-10-01

316

Interaction of a Type Ia Supernovae with Circumstellar Mass  

NASA Astrophysics Data System (ADS)

We study the radiation signatures of a type Ia supernova interacting with circumstellar mass (CSM) of various configurations. Although it is hypothesized that type Ia supernovae originate from binary systems with one star donating mass to a carbon-oxygen white dwarf, the nature of the mass donor companion remains a mystery. One way to distinguish the companion is from signatures of the supernova colliding with CSM created by the mass transfer mechanism (e.g. nova shells, wind). CSM is rarely observed, which may be a challenge for different models to explain. In a one-dimensional hydrodynamical simulation, we collide a normal type Ia supernova with CSM of various configurations (e.g. composition, position, density) and calculate various radiation signatures for each case, such as synchrotron, X-ray signal, and hydrogen line luminosity. With this we can study degeneracies between different CSM configurations, accurately calculate the radiation signature of a shell, guide observational tests, and interpret existing observations of interacting supernovae.

Harris, Chelsea; Nugent, Peter E.; Kasen, Daniel; Roth, Nathaniel

2015-01-01

317

A WISE Survey of Circumstellar Disks in Taurus  

E-print Network

We have compiled photometry at 3.4, 4.6, 12 and 22 $\\mu$m from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1 - M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than $\\sim$M8 ($M \\gtrsim 0.03$ $M_\\odot$).

Esplin, T L; Mamajek, E E

2014-01-01

318

Episodic Mass Loss and Pre-SN Circumstellar Envelopes  

E-print Network

I discuss observational clues concerning episodic mass-loss properties of massive stars in the time before the final supernova explosion. In particular, I will focus on the mounting evidence that LBVs and related stars are candidates for supernova progenitors, even though current paradigms place them at the end of core-H burning. Namely, conditions in the immediate circumstellar environment within a few 10$^2$ AU of Type IIn supernovae require very high progenitor mass-loss rates. Those rates are so high that the only known stars that come close are LBVs during rare giant eruptions. I will highlight evidence from observations of some recent extraordinary supernovae suggesting that explosive or episodic mass loss (a.k.a. LBV eruptions like the 19th century eruption of Eta Car) occur in the 5-10 years immediately preceding the SN. Finally, I will discuss some implications for stellar evolution from these SNe, the most important of which is the observational fact that the most massive stars can indeed make it to the ends of their lives with substantial H envelopes intact, even at Solar metallicity.

Nathan Smith

2008-02-13

319

Studying Prokaryotic Communities in Iron Depositing Hot Springs (IDHS): Implication for Early Mars Habitability  

NASA Technical Reports Server (NTRS)

We speculate that both external and intracellular iron precipitate in iron-tolerant CB might be involved in oxidative stress suppression shown by [9]. Significant differences are apparent between a set of proteins involved in the maintenance of Fe homeostasis and oxidative stress protection in iron-tolerant and fresh-water and marine CB. Correspondingly, these properties may help to make iron-tolerant CB as dominant organisms in IDHS and probably on early Earth and Mars. Further comparative analyses of hot springs metagenomes and the genomes of iron-tolerant microbes versus fresh-water/marine ones may point out to different habitable zones on early Mars.

Sarkisova, S. A.; Tringe, S. G.; Thomas-Keprta, K. L.; Allen, C. c.; Garrison, D. H.; McKay, David S.; Brown, I. I.

2010-01-01

320

An Astrobiological Experiment to Explore the Habitability of Tidally Locked M-Dwarf Planets  

NASA Astrophysics Data System (ADS)

We present a summary of a three-year academic research proposal drafted during the Sao Paulo Advanced School of Astrobiology (SPASA) to prepare for upcoming observations of tidally locked planets orbiting M-dwarf stars. The primary experimental goal of the suggested research is to expose extremophiles from analogue environments to a modified space simulation chamber reproducing the environmental parameters of a tidally locked planet in the habitable zone of a late-type star. Here we focus on a description of the astronomical analysis used to define the parameters for this climate simulation.

Angerhausen, Daniel; Sapers, Haley; Simoncini, Eugenio; Lutz, Stefanie; Alexandre, Marcelo da Rosa; Galante, Douglas

2014-04-01

321

Habitability in Advanced Space Mission Design. Part 2; Evaluation of Habitation Elements  

NASA Technical Reports Server (NTRS)

Habitability is a fundamental component of any long-duration human habitat. Due to the pressures on the crew and the criticality of their performance, this is particularly true of habitats or vehicles proposed for use in any human space mission of duration over 30 days. This paper, the second of three on this subject, will focus on evaluating all the vehicles currently under consideration for the Mars Design Reference Mission through application of metrics for habitability (proposed in a previous paper, see references Adams/McCurdy 1999).

Adams, Constance M.; McCurdy, Matthew R.

2000-01-01

322

Formation, tidal evolution and habitability of the Kepler-186 system  

E-print Network

The Kepler-186 system consists of five planets orbiting an early-M dwarf. The planets have physical radii of 1.0-1.50 R$_\\oplus$ and orbital periods of 4 to 130 days. The $1.1~$R$_\\oplus$ Kepler-186f with a period of 130 days is of particular interest. Its insolation of roughly $0.32~S_\\odot$places it within the liquid water habitable zone. We present a multi-faceted study of the Kepler-186 system. First, we show that the distribution of planet masses can be roughly reproduced if the planets accreted from a high-surface density disk presumably sculpted by an earlier phase of migration. However, our simulations predict the existence of 1-2 undetected planets between planets e and f. Next, we present a dynamical analysis of the system including the effect of tides. The timescale for tidal evolution is short enough that the four inner planets must have small obliquities and near-synchronous rotation rates. Tidal evolution of Kepler-186f is slow enough that its current spin state depends on a combination of its d...

Bolmont, Emeline; von Paris, Philip; Selsis, Franck; Hersant, Franck; Quintana, Elisa V; Barclay, Thomas

2014-01-01

323

Assessing habitability of aqueous environments on Mars  

NASA Astrophysics Data System (ADS)

A source of metabolic energy is a requirement for life. One possible source of energy that may have supported potential organisms on Mars was geochemical energy from chemical disequilibrium. We evaluated the habitability of aqueous environments on Mars by quantifying the amount of available geochemical energy from chemosynthetic reactions from a range of martian environments. By determining the overall Gibbs energy yields for redox reactions in the H-O-C-S-Fe system, the amount of geochemical energy that was available for potential chemolithoautotrophic microorganisms was quantified and the amount of biomass that could have been sustained was estimated. Biomass estimates show that Fe and S redox reactions in basalt aquifers may have supported the production of 1012 cells of biomass per kg of altered basalt. Additionally, a putative martian subsurface hydrothermal system would have had the potential to support a maximum of 109 cells per kilogram of vent fluid. The geochemical models indicate that aqueous environments on Mars would have had the potential to generate chemical energy sources to allow for habitable environments, and potential populations of organisms at subsurface hydrothermal systems on Mars would have been approximately two orders of magnitude less than what was modeled for terrestrial hydrothermal systems. Furthermore, the results were applied to four of the Mars Science Laboratory potential landing sites in order to assess which sites may have had the most biological potential. The most habitable sites are considered here to be Gale Crater and Marwth Vallis based on mineralogical evidence with various oxidation states of Fe and S.

Tierney, Lindsey Link

324

Habitability of super-Earth planets around other suns: models including Red Giant Branch evolution.  

PubMed

The unexpected diversity of exoplanets includes a growing number of super-Earth planets, i.e., exoplanets with masses of up to several Earth masses and a similar chemical and mineralogical composition as Earth. We present a thermal evolution model for a 10 Earth-mass planet orbiting a star like the Sun. Our model is based on the integrated system approach, which describes the photosynthetic biomass production and takes into account a variety of climatological, biogeochemical, and geodynamical processes. This allows us to identify a so-called photosynthesis-sustaining habitable zone (pHZ), as determined by the limits of biological productivity on the planetary surface. Our model considers solar evolution during the main-sequence stage and along the Red Giant Branch as described by the most recent solar model. We obtain a large set of solutions consistent with the principal possibility of life. The highest likelihood of habitability is found for "water worlds." Only mass-rich water worlds are able to realize pHZ-type habitability beyond the stellar main sequence on the Red Giant Branch. PMID:19630504

von Bloh, W; Cuntz, M; Schröder, K-P; Bounama, C; Franck, S

2009-01-01

325

TRAPPIST-UCDTS: A prototype search for habitable planets transiting ultra-cool stars  

NASA Astrophysics Data System (ADS)

The ˜1000 nearest ultra-cool stars (spectral type M6 and latter) represent a unique opportunity for the search for life outside solar system. Due to their small luminosity, their habitable zone is 30-100 times closer than for the Sun, the corresponding orbital periods ranging from one to a few days. Thanks to this proximity, the transits of a habitable planet are much more probable and frequent than for an Earth-Sun analog, while their tiny size (˜1 Jupiter radius) leads to transits deep enough for a ground-based detection, even for sub-Earth size planets. Furthermore, a habitable planet transiting one of these nearby ultra-cool star would be amenable for a thorough atmospheric characterization, including the detection of possible biosignatures, notably with the near-to-come JWST. Motivated by these reasons, we have set up the concept of a ground-based survey optimized for detecting planets of Earth-size and below transiting the nearest Southern ultra-cool stars. To assess thoroughly the actual potential of this future survey, we are currently conducting a prototype mini-survey using the TRAPPIST robotic 60cm telescope located at La Silla ESO Observatory (Chile). We summarize here the preliminary results of this mini-survey that fully validate our concept.

Gillon, M.; Jehin, E.; Fumel, A.; Magain, P.; Queloz, D.

2013-04-01

326

Food habits of bobcats in eastern Tennessee  

SciTech Connect

Food habits of bobcats (Lynx rufus) in eastern Tennessee were determined from analyzing 176 cat samples collected on the Oak Ridge National Environmental Research Park. Remains of cottontail rabbits (Sylvilagus floridanus) were the most frequently occurring food item. White-tail deer (Odocoileus virginianus) and pine vole (Microtus pinetorum) remains also were found frequently in samples. Data obtained from this study indicated that food preferences for bobcats in eastern Tennessee are similar to those in other southeastern states where the habitat is similar to the Oak Ridge area and somewhat different from those with significantly different habitat.

Story, J.D.; Galbraith, W.J.; Kitchings, J.T.

1982-01-01

327

Health habits of patients with schizophrenia  

Microsoft Academic Search

Background  The aim of the study was to analyze the physical activity, dietary, drinking, and smoking habits of schizophrenia patients\\u000a (SP).\\u000a \\u000a \\u000a \\u000a Methods  Data from 194 schizophrenia outpatients collected using sections of the German National Health Interview and Examination Survey\\u000a were compared with data from the German general population (GP). In addition to univariate data analyses, a multivariate regression\\u000a analysis was performed.\\u000a \\u000a \\u000a \\u000a Results  Schizophrenia

Christiane Roick; Anita Fritz-Wieacker; Herbert Matschinger; Dirk Heider; Jana Schindler; Steffi Riedel-Heller; Matthias C. Angermeyer

2007-01-01

328

Habit formation: implications for alcoholism research.  

PubMed

Characteristics of individuals with severe alcohol use disorders include heightened cue sensitivity, compulsive seeking, craving, and continued alcohol use in the face of negative consequences. Animal models are useful for understanding behavioral and neurological mechanisms underlying problematic alcohol use. Seeking of operant reinforcers including alcohol is processed by two mechanisms, commonly referred to as "goal-directed" (action-outcome) and "habitual" (stimulus-response). As substance use disorders are characterized by continued use regardless of unfavorable outcomes, it is plausible that drug use causes an unnatural disruption of these mechanisms. We present a critical analysis of literature pertaining to behavioral neuroscience alcoholism research involving habit formation. Traditionally, when operant behavior is unaffected by a loss of subjective value of a reinforcer (devaluation), the behavior is considered habitual. Acquisition of instrumental behavior requires corticostriatal mechanisms that depend heavily on the prefrontal cortex and ventral striatum, whereas practiced behavior is more predominantly controlled by the dorsal striatum. Dopaminergic signaling is necessary for the neurological adaptations involved in stimulus-response action, and drugs of abuse appear to facilitate habitual behavior through high levels of dopamine release. Evidence suggests that the use of alcohol as a reinforcer expedites habit formation, and that a history of alcohol use produces alterations in striatal morphology, aids habit learning for non-psychoactive reinforcers, and promotes alcohol drinking despite aversive adulterants. In this review, we suggest directions for future alcoholism research that seeks to measure action made despite a devalued outcome, including procedural modifications and genotypic, pharmacological, or neurological manipulations. Most alcoholism models currently in use fail to reach substantial blood ethanol concentrations, a shortcoming that may be alleviated through the use of high-drinking rodent lines. Additionally, satiety, one common mechanism of devaluing reinforcers, is not recommended for alcohol research because the psychoactive effects of alcohol depress response rates, mimicking devaluation effects. Overall, further research of habit formation and potentially related perseverative behaviors could be invaluable in discovering genetic variance, traits that correlate with persistent alcohol seeking, implicated neural structures and processes of alcohol use, and eventually novel pharmacological treatment for alcoholism. PMID:24835007

O'Tousa, David; Grahame, Nicholas

2014-06-01

329

Habitability issues in long duration undersea and space missions  

NASA Technical Reports Server (NTRS)

The report reviews a number of studies in the area of habitability. Emphasis was placed on extracting from these studies that information most relevant to any long-term mission in confinement. It is concluded that, whereas the basic laws of habitability are known, there is much yet to be learned concerning development of social structures in small groups in relative isolation, planning for necessary hygiene needs, development of proper work spaces, and construction of internal and external communications systems. With respect to testing for habitability and the documentation of habitability principles, the space program was found to be considerably more advanced than was the program for undersea missions.

Parker, J. F., Jr.; Every, M. G.

1972-01-01

330

Circumstellar medium around rotating massive stars at solar metallicity  

NASA Astrophysics Data System (ADS)

Aims: Observations show nebulae around some massive stars but not around others. If observed, their chemical composition is far from homogeneous. Our goal is to put these observational features into the context of the evolution of massive stars and their circumstellar medium (CSM) and, more generally, to quantify the role of massive stars for the chemical and dynamical evolution of the ISM. Methods: Using the A-MAZE code, we perform 2d-axisymmetric hydrodynamical simulations of the evolution of the CSM, shaped by stellar winds, for a whole grid of massive stellar models from 15 to 120 M? and following the stellar evolution from the zero-age main-sequence to the time of supernova explosion. In addition to the usual quantities, we also follow five chemical species: H, He, C, N, and O. Results: We show how various quantities evolve as a function of time: size of the bubble, position of the wind termination shock, chemical composition of the bubble, etc. The chemical composition of the bubble changes considerably compared to the initial composition, particularly during the red-supergiant (RSG) and Wolf-Rayet (WR) phases. In some extreme cases, the inner region of the bubble can be completely depleted in hydrogen and nitrogen, and is mainly composed of carbon, helium, and oxygen. We argue why the bubble typically expands at a lower rate than predicted by self-similarity theory. In particular, the size of the bubble is very sensitive to the density of the ISM, decreasing by a factor of ~2.5 for each additional dex in ISM density. The bubble size also decreases with the metallicity of the central star, because low-metallicity stars have weaker winds. Our models qualitatively fit the observations of WR ejecta nebulae.

Georgy, Cyril; Walder, Rolf; Folini, Doris; Bykov, Andrei; Marcowith, Alexandre; Favre, Jean M.

2013-11-01

331

STELLAR AND CIRCUMSTELLAR PROPERTIES OF CLASS I PROTOSTARS  

SciTech Connect

We present a study of the stellar and circumstellar properties of Class I sources using low-resolution (R {approx} 1000) near-infrared (near-IR) K- and L-band spectroscopy. We measure prominent spectral lines and features in eight objects and use fits to standard star spectra to determine spectral types, visual extinctions, K-band excesses, and water ice optical depths. Four of the seven systems studied are close binary pairs; only one of these systems, Haro 6-10, was angularly resolvable. For certain stars, some properties found in our analysis differ substantially from published values; we analyze the origin of these differences. We determine extinction to each source using three different methods and compare and discuss the resulting values. One hypothesis that we were testing, that extinction dominates over the K-band excess in obscuration of the stellar photospheric absorption lines, appears not to be true. Accretion luminosities and mass accretion rates calculated for our targets are highly uncertain, in part the result of our inexact knowledge of extinction. For the six targets we were able to place on a Hertzsprung-Russell diagram, our age estimates, <2 Myr, are somewhat younger than those from comparable studies. Our results underscore the value of low-resolution spectroscopy in the study of protostars and their environments; however, the optimal approach to the study of Class I sources likely involves a combination of high- and low-resolution near-IR, mid-IR, and millimeter wavelength observations. Accurate and precise measurements of extinction in Class I protostars will be key to improving our understanding of these objects.

Prato, L.; Lockhart, K. E. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Johns-Krull, Christopher M. [Department of Physics and Astronomy, Rice University, MS-108, 6100 Main Street, Houston, TX 77005 (United States); Rayner, John T. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)], E-mail: lprato@lowell.edu, E-mail: k.e.lockhart@gmail.com, E-mail: cmj@rice.edu, E-mail: rayner@ifa.hawaii.edu

2009-04-15

332

Thermal desorption of circumstellar and cometary ice analogs  

NASA Astrophysics Data System (ADS)

Context. Thermal annealing of interstellar ices takes place in several stages of star formation. Knowledge of this process comes from a combination of astronomical observations and laboratory simulations under astrophysically relevant conditions. Aims: For the first time we present the results of temperature programmed desorption (TPD) experiments with pre-cometary ice analogs composed of up to five molecular components: H2O, CO, CO2, CH3OH, and NH3. Methods: The experiments were performed with an ultra-high vacuum chamber. A gas line with a novel design allows the controlled preparation of mixtures with up to five molecular components. Volatiles desorbing to the gas phase were monitored using a quadrupole mass spectrometer, while changes in the ice structure and composition were studied by means of infrared spectroscopy. Results: The TPD curves of water ice containing CO, CO2, CH3OH, and NH3 present desorption peaks at temperatures near those observed in pure ice experiments, volcano desorption peaks after water ice crystallization, and co-desorption peaks with water. Desorption peaks of CH3OH and NH3 at temperatures similar to the pure ices takes place when their abundance relative to water is above ~3% in the ice matrix. We found that CO, CO2, and NH3 also present co-desorption peaks with CH3OH, which cannot be reproduced in experiments with binary water-rich ice mixtures. These are extensively used in the study of thermal desorption of interstellar ices. Conclusions: These results reproduce the heating of circumstellar ices in hot cores and can be also applied to the late thermal evolution of comets. In particular, TPD curves represent a benchmark for the analysis of the measurements that mass spectrometers on board the ESA-Rosetta cometary mission will perform on the coma of comet 67P/Churyumov-Gerasimenko, which will be active before the arrival of Rosetta according to our predictions.

Martín-Doménech, R.; Muñoz Caro, G. M.; Bueno, J.; Goesmann, F.

2014-04-01

333

Investigations of the Formation of Carbon Grains in Circumstellar Outflows  

NASA Technical Reports Server (NTRS)

The study of formation and destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic molecules. Although dust with all its components plays an important role in the evolution of interstellar chemistry and in the formation of organic molecules, little is known on the formation and destruction processes of carbonaceous dust. PAHs are important chemical building blocks of interstellar dust. They are detected in interplanetary dust particles and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs, in their neutral and ionized forms, are an important, ubiquitous component of the interstellar medium. Also, the formation of PAHs from smaller molecules has not been extensively studied. Therefore, it is imperative that laboratory experiments be conducted to study the dynamic processes of carbon grain formation from PAH precursors. Studies of interstellar dust analogs formed from a variety of PAH and hydrocarbon precursors as well as species that include the atoms O, N, and S, have recently been performed in our laboratory under conditions that simulate interstellar and circumstellar environments. The species formed in the pulsed discharge nozzle (PDN) plasma source are detected and characterized with a high-sensitivity cavity ringdown spectrometer (CRDS) coupled to a Reflectron time-of-flight mass spectrometer (ReTOF-MS), thus providing both spectroscopic and ion mass information in-situ. We report the first set of measurements obtained in these experiments and identify the species present in the experiments and the ions that are formed in the plasma process. From these unique measurements, we derive information on the size and the structure of interstellar dust grain particles, the growth and the destruction processes of interstellar dust and the resulting budget of extraterrestrial organic molecules.

Contreras, Cesar; Salama, Farid

2013-01-01

334

High Resolution Submillimeter Constraints on Circumstellar Disk Structure  

E-print Network

We present a high spatial resolution submillimeter continuum survey of 24 circumstellar disks in the Tau-Aur and Oph-Sco star formation regions using the SMA. In the context of a simple model, we use broadband SEDs and submillimeter visibilities to derive constraints on some basic parameters that describe the structure of these disks. For the typical disk in the sample we infer a radial surface density distribution \\Sigma ~ r^-p with a median p ~ 0.5, although consideration of the systematic effects of some of our assumptions suggest that steeper distributions with p ~ 0.7-1.0 are more reasonable. The distribution of the outer radii of these disks shows a distinct peak at R_d = 200 AU, with only a few cases where the disk emission is completely unresolved. Based on these disk structure measurements, the mass accretion rates, and the typical spectral and spatial distributions of submillimeter emission, we show that the observations are in good agreement with similarity solutions for steady accretion disks that have a viscosity parameter alpha ~ 0.01. We provide new estimates of the spectral dependence of the disk opacity with a median spectral index of ~0.7, corrected for optically thick emission. This typical value is consistent with model predictions for the collisional growth of solids to millimeter size scales in the outer disk. Although direct constraints on planet formation in these disks are not currently available, the extrapolated density distributions inferred here are substantially shallower than those calculated based on the solar system or extrasolar planets and typically used in planet formation models. It is possible that we are substantially underestimating disk densities due to an incomplete submillimeter opacity prescription.

Sean M. Andrews; Jonathan P. Williams

2006-10-27

335

Planetary Habitability and Rapid Environmental Change: The Biological Perspective  

NASA Astrophysics Data System (ADS)

Environmental conditions can change drastically and rapidly during the natural history of a planetary body. We have detailed evidence of these dramatic events from Venus, Earth, Mars, and Titan. Most of these occurrences seem to be triggered by astronomical events such as asteroid impacts or supernova explosions; others are triggered by the planet or moon itself (e.g., supervolcano eruptions). The associated question is always how these events affect the habitability of a planet, particularly the origin and presence of life. Under what conditions would such a drastic event be so catastrophic that it would prohibit the origin of life or be so devastating to existing organisms, that life would not be able to recover and be all but extinguished from a planet? Under what conditions would such an event be positive for the evolution of life, for example spurring life via mass extinctions and associated vacant habitats to the invention of new body plans and higher complexity? Here, we provide insights of what we can learn from the natural history of our own planet, which experienced many environmental disasters and abrupt climate changes, from the impact event that created the Moon to the extinction of the dinosaurs. We apply these insights to other planetary bodies and the question about the presence of life. One example is Mars, which underwent drastic environmental changes at the end of the Noachian period. Assuming that microbial life became established on Mars, could it have survived, perhaps by retreating to environmental niches? Life just starting out would have certainly been more vulnerable to extinction. But how far would it have to have evolved to be more resistant to potential extinction events? Would it have to be global in distribution to survive? Another example is Venus. Should Venus be seen as an example where life, which possibly arose in the first few hundred million years when the planet was still in the habitable zone, would have had no chance to survive the upcoming calamities (e.g., the putative meteorite impact that resulted in an opposite spin of the planet, global volcanic eruptions, a run-away greenhouse effect, etc)? Titan may be the most exotic example. Titan may have experienced the transition from a warmer, water-based solvent to a colder, hydrocarbon-based solvent early in its natural history and is still undergoing climate-change cycles. What effects would these transitions have on a possible biosphere? These insights will be also critical for assessing the possibility of life on any "Super-Earth" and other exoplanets, including an assessment of the limits to which life can adapt.

Schulze-Makuch, D.; Fairen, A.; Irwin, L.

2012-12-01

336

Late-stage accretion and habitability of terrestrial planets  

NASA Astrophysics Data System (ADS)

The final stage in the formation of terrestrial planets consists of the accumulation of ~1000 km "planetary embryos" and ~1 km planetesimals via collisional accretion., under the mutual gravity of other solid bodies and the gas giant planets (if any). Water is delivered to planets via collisions with volatile-rich bodies that condensed past the snow line, beyond about 2.5 AU. We present results of a large number of relatively low-resolution simulations, designed to assess the predictability of systems of terrestrial planets as a function of "observables" such as the orbit of gas giant planets. These show that a variety of terrestrial planets can form, from small, dry, Mars-like worlds to planets with similar properties to Earth, to >3 Earth mass "water worlds" with >=30 times as much water as the Earth. The terrestrial planets are largely shaped by the influence of the giant planets and the surface density of material. We have uncovered trends between the terrestrial planets and (i) the mass, (ii) the orbital distance and (iii) the orbital eccentricity of a giant planet, (iv) the surface density of the disk, and (v) the disk's density profile. Five simulations with 1000-2000 particles reveal new aspects of the accretion process Water is delivered to the terrestrial planets as a few large planetesimals in a "hit or miss" process, and as billions of planetesimals in a robust way. The water delivery process is therefore more robust than previously thought, implying that the range of water contents of extra-solar Earths is less stochastic than indicated in previous studies; most planets accrete water- rich bodies. We simulate terrestrial accretion in the presence of close-in giant planets (e.g., "hot jupiters"), assuming these form and migrate quickly. Potentially habitable planets can form in these systems, but are likely to be iron-poor. Asteroid belts may exist between the terrestrial planets and hot jupiters in these systems. We have also tested the accretion process in four known extra- solar planetary systems. In 55 Cancri, terrestrial planets form relatively easily, and may have orbits in the habitable zone and significant water contents.

Raymond, Sean Neylon

337

Inflatable habitation for the lunar base  

NASA Technical Reports Server (NTRS)

Inflatable structures have a number of advantages over rigid modules in providing habitation at a lunar base. Some of these advantages are packaging efficiency, convenience of expansion, flexibility, and psychological benefit to the inhabitants. The relatively small, rigid cylinders fitted to the payload compartment of a launch vehicle are not as efficient volumetrically as a collapsible structure that fits into the same space when packaged, but when deployed is much larger. Pressurized volume is a valuable resource. By providing that resource efficiently, in large units, labor intensive external expansion (such as adding additional modules to the existing base) can be minimized. The expansive interior in an inflatable would facilitate rearrangement of the interior to suite the evolving needs of the base. This large, continuous volume would also relieve claustrophobia, enhancing habitability and improving morale. The purpose of this paper is to explore some of the aspects of inflatable habitat design, including structural, architectural, and environmental considerations. As a specific case, the conceptual design of an inflatable lunar habitat, developed for the Lunar Base Systems Study at the Johnson Space Center, is described.

Roberts, M.

1992-01-01

338

The Structure and Evolution of Circumstellar Disks Revealed by Mid-Infrared Interferometry  

NASA Astrophysics Data System (ADS)

Circumstellar discs transport angular momentum, serve as reservoir from which the central stars accrete gas and dust, and are the sites where planets form. The evolution of these discs, however, is only coarsely known today. For a better understanding it is essential to resolve the distribution and composition of the dust in the discs' warm, inner parts. Differences between the circumstellar discs of the components of binary systems provide further insights. With the 10 - 20 milli-arcsec spatial resolution offered by the MID-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) we were able to resolve the circumstellar disks of several low-mass young stellar objects, e.g., T Tau, GV Tau, SVS 20, and TW Hya. The spectrally dispersed interferometric data in the wavelength range between 8 and 13 micron are also well suited to study radial changes of the dust composition and grain growth, a prerequisite for planet formation.

Ratzka, Thorsten; Roccatagliata, Veronica; Grellmann, Rebekka; Köhler, Rainer

2013-07-01

339

Progenitors of Type Ia Supernovae: Circumstellar Interaction, Rotation, and Steady Hydrogen Burning  

E-print Network

Among the important issues in identifying the progenitor system of Type Ia supernovae (SNe Ia), we focus mostly on circumstellar interaction in SN 2002ic, and give brief discussion on the controversial issues of the effects of rotation in merging double degenerates and steady hydrogen shell burning in accreting white dwarfs. SN 2002ic is a unique supernova which shows the typical spectral features of SNe Ia near maximum light, but also apparent hydrogen features that have been absent in SNe Ia. Based on the hydrodynamical models of circumstellar interaction in SN Ia, we suggest that circumstellar medium is aspherical (or highly clumpy) and contains ~1.3 Msun. Possible progenitor systems of SN 2002ic are discussed.

Ken'ichi Nomoto; Tomoharu Suzuki; Jinsong Deng; Tatsuhiro Uenishi; Izumi Hachisu

2006-03-16

340

For Parents Particularly: Learning Healthful Habits for a Lifetime.  

ERIC Educational Resources Information Center

Provides several suggestions to parents willing to help their children understand the importance of developing and practicing healthful habits. Discusses advantages of washing hands regularly and thoroughly and developing good oral hygiene. Urges parents to practice and teach healthful habits and become models for their children. (AA)

Newman, Rita

1997-01-01

341

Activating & Engaging Habits of Mind. A Developmental Series, Book 2.  

ERIC Educational Resources Information Center

This book is the second in a four-book series on habits of mind. It translates a habits of mind approach to education into action using classroom-tested advice. Contributions come from practitioners in literature, math, music, foreign language, reading, character education, and social science. After "Series Foreword: Thinking on the Road of Life"…

Costa, Arthur L., Ed.; Kallick, Bena, Ed.

342

Primary School Teacher Candidates' Geometric Habits of Mind  

ERIC Educational Resources Information Center

Geometric habits of mind are productive ways of thinking that support learning and using geometric concepts. Identifying primary school teacher candidates' geometric habits of mind is important as they affect the development of their future students' geometric thinking. Therefore, this study attempts to determine primary school…

Köse, Nilu¨fer Y.; Tanisli, Dilek

2014-01-01

343

Literacy Attitudes, Habits and Achievements of Future Teachers  

ERIC Educational Resources Information Center

Pre-service teachers' reading habits and their literacy abilities affect their views toward teaching reading and writing and how they implement literacy instruction. This study explored the relationship between the past and current reading habits of pre-service teachers in relation to their reading and writing abilities. Participating teacher…

Benevides, Tina; Stagg Peterson, Shelley

2010-01-01

344

Dietary Habits Prone to Lifestyle-Related Disease  

ERIC Educational Resources Information Center

Objective: To evaluate relations among dietary habits, bone mineral density (BMD), visceral fat area (VFA), and arterial stiffness and recommend better dietary habits. Methods: One hundred and six men and 381 women (aged 18-84) received a health checkup and answered questionnaires, with subsequent measurements of BMD (speed of sound), VFA…

Nagai, M.; Uyama, O.; Kaji, H.

2013-01-01

345

Calculating the Number of Habitable Planets in the Milky Way  

Microsoft Academic Search

It is traditional to discuss about extraterrestrial intelligence in terms of the celebrated Drake equation, with its estimates of habitable planetary systems, origins of life, evolution of technology, and so on. Although several factors are highly speculative, a subset of them, describing the number of habitable planets can be now stated more precisely with the help of new results from

Siegfried Franck; Werner Bloh; Christine Bounama; Hans-Joachim Schellnhuber

346

Computer Habits and Behaviours among Young Children in Singapore  

ERIC Educational Resources Information Center

This exploratory research project was aimed at developing baseline data on computer habits and behaviours among preschool children in Singapore. Three sets of data were collected from teachers, parents and children which are (1) why and how young children use computers; (2) what are the key physical, social and health habits and behaviours of…

Karuppiah, Nirmala

2015-01-01

347

Intergenerational and Urban-Rural Health Habits in Chinese Families  

ERIC Educational Resources Information Center

Objective: To explore intergenerational health habits and compare differences between urban and rural families. Methods: A total of 2500 families with children ages 6-18 in China were surveyed regarding their health habits. Results: Urban families reported significantly greater food variety and more time exercising (for fathers and children) than…

Li, Li; Lin, Chunqing; Cao, Haijun; Lieber, Eli

2009-01-01

348

Radiological Habits Survey: Dumfries and Galloway Coast, 2012  

E-print Network

Radiological Habits Survey: Dumfries and Galloway Coast, 2012 #12;This page has been intentionally left blank #12;Environment Report RL 25/13 Final report Radiological Habits Survey: Dumfries This report should be cited as: Garrod, C.J., Clyne, F.J., Ly, V.E. and Papworth, G.P., 2013. Radiological

349

Association of Hypoadiponectinemia With Smoking Habit in Men  

Microsoft Academic Search

Adiponectin is emerging as an important molecule in obesity, the metabolic syndrome, and cardiovascular disease. On the other hand, smoking habit is well known to be related to cardiovascular disease and hypertension. To examine the association between adiponectin concentration and smoking habit, we performed an epidemiological survey and an acute exposure test in humans and an experiment in adipocytes to

Yoshio Iwashima; Tomohiro Katsuya; Kazuhiko Ishikawa; Iwao Kida; Mitsuru Ohishi; Takeshi Horio; Noriyuki Ouchi; Koji Ohashi; Shinji Kihara; Tohru Funahashi; Hiromi Rakugi; Toshio Ogihara

2010-01-01

350

Duty, Habit, and Meaning: Different Faces of Adherence.  

ERIC Educational Resources Information Center

All elements of an active lifestyle need not be meaningful. Good active habits of living can be generated without significant reliance on excitement or other kinds of notable meaning. The development of active living habits depend partly on enlightened social policy, but such policies are rare in the United States. Consequently, kinesiologists…

Kretchmar, R. Scott

2001-01-01

351

Measuring Study Habits in Higher Education: The Way Forward?  

NASA Astrophysics Data System (ADS)

This article reviews existing study habit measurement instruments and discusses their drawbacks, in the light of new evidence from neuroscience on the workings of the brain. It is suggested that in addition to traditional frequency based past behavioural measures, the predictive accuracy of study habit measurement instruments could be improved by including measures of habit strength that take into account behaviour automaticity and efficacy, such as the Self-Report Habit Index (SRHI) developed by [1]. The SRHI has shown high reliability and internal validity in a wide range of contexts and its applicability and validity in the context of learning and higher education as an enhancement to study habit measurement instruments is as yet to be tested.

Fitkov-Norris, E. D.; Yeghiazarian, A.

2013-09-01

352

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

353

Structure and evolution of circumstellar disks: A Spitzer view  

NASA Astrophysics Data System (ADS)

This dissertation is the sum of five studies of the structure and evolution of circumstellar disks, the birthplace of planets. These studies are all based on Infrared data from the Spitzer Space Telescope, and taken together trace the evolution of disks from the optically thick primordial stage to the optically thin debris disk stage. The five projects included in this dissertation are diverse but they are all interconnected and have a common underlying motivation: to impose observational constraints on different aspects of planet formation theories. In the first project, we study the near and mid-IR (1.2-24 mm) emission of Classical T Tauri Star (CTTS), which are low-mass pre-main sequence (PMS) stars that show clear evidence for accretion. We discuss the implications of our results on the structure of their inner disks and their estimated ages. In the second project, we study the incidence as a function of age of disks around weak-line T Tauri stars (low-mass PMS stars that are mostly coeval with CTTS but that do not show clear evidence for accretion) and explore the structure of these disks. We estimate the dissipation timescale of the planet-forming region of primordial disks and discuss the implications for planet formation theories. The third and fourth projects deal with the evolution of angular momentum of PMS stars. We search for observational evidence for the connection between stellar rotation and the presence of a disk predicted by the current disk-braking paradigm, according to which the rotational evolution of PMS stars is regulated through magnetic interactions between the stellar magnetosphere and the inner disk. The last project deals with debris disks, which are second-generation disks where the dust is continuously replenished by collisions between planetesimals. We search for debris disks in the far-IR (24-160 mm) around a sample of Hyades Cluster members. We discuss the implications of our results on the evolution of debris disks and on the Late Heavy Bombardment in the Solar System.

Cieza-Gonzalez, Lucas Alejo

354

TYPE Ia SUPERNOVAE STRONGLY INTERACTING WITH THEIR CIRCUMSTELLAR MEDIUM  

SciTech Connect

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{alpha} emission (with widths of {approx}2000 km s{sup -1}) and exhibit large H{alpha}/H{beta} 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{alpha} 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 {<=} M{sub R} {<=} -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. [Department of Astronomy, University of Texas, Austin, TX 78712-0259 (United States); Nugent, Peter E. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Gal-Yam, Avishay; Arcavi, Iair; Ben-Ami, Sagi [Benoziyo Center for Astrophysics, Weizmann Institute of Science, Rehovot 76100 (Israel); Sullivan, Mark [School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom); Howell, D. Andrew; Graham, Melissa L. [Las Cumbres Observatory Global Telescope Network, Goleta, CA 93117 (United States); Filippenko, Alexei V.; Bloom, Joshua S.; Cenko, S. Bradley; Clubb, Kelsey I. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Cao, Yi; Horesh, Assaf; Kulkarni, Shrinivas R. [Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Chornock, Ryan; Foley, Ryan J. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Coil, Alison L. [Department of Physics, University of California, San Diego, La Jolla, CA 92093 (United States); Griffith, Christopher V. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Kasliwal, Mansi M., E-mail: jsilverman@astro.as.utexas.edu [Observatories of the Carnegie Institution of Science, Pasadena, CA 91101 (United States); and others

2013-07-01

355

The quantitative modelling of human spatial habitability  

NASA Technical Reports Server (NTRS)

A model for the quantitative assessment of human spatial habitability is presented in the space station context. The visual aspect assesses how interior spaces appear to the inhabitants. This aspect concerns criteria such as sensed spaciousness and the affective (emotional) connotations of settings' appearances. The kinesthetic aspect evaluates the available space in terms of its suitability to accommodate human movement patterns, as well as the postural and anthrometric changes due to microgravity. Finally, social logic concerns how the volume and geometry of available space either affirms or contravenes established social and organizational expectations for spatial arrangements. Here, the criteria include privacy, status, social power, and proxemics (the uses of space as a medium of social communication).

Wise, J. A.

1985-01-01

356

The habitable epoch of the early Universe  

NASA Astrophysics Data System (ADS)

In the redshift range 100<~(1+z)<~137, the cosmic microwave background (CMB) had a temperature of 273-373 K (0-100°C), allowing early rocky planets (if any existed) to have liquid water chemistry on their surface and be habitable, irrespective of their distance from a star. In the standard ?CDM cosmology, the first star-forming halos within our Hubble volume started collapsing at these redshifts, allowing the chemistry of life to possibly begin when the Universe was merely 10-17 million years old. The possibility of life starting when the average matter density was a million times bigger than it is today is not in agreement with the anthropic explanation for the low value of the cosmological constant.

Loeb, Abraham

2014-09-01

357

The organism and the habitation atmosphere  

NASA Technical Reports Server (NTRS)

Experimental data is examined on the study of the influence of the different parameters of the atmosphere on the organism for the purpose of making a physiological determination of the permissible oxygen concentrations in inhabited airtight compartments. The application of high oxygen concentrations for respiration and for medical purposes are considered. Data is presented on the evolution of the atmosphere and of the role of O2 in the process of the evolutionary development of living beings; the influence of an organism of an artificial, high and low oxygen concentration atmospheres; the laws of oxygen permeation into fluid media of the organism; the biological role of inert gases; etc. The relationship between the gas medium of habitation and reactivity of the organism is determined.

Agadzhanyan, N. A.

1978-01-01

358

Infrared circumstellar shells - Origins, and clues to the evolution of massive stars  

NASA Technical Reports Server (NTRS)

The infrared fluxes, spatial and spectral characteristics for a sample of 111 supergiant stars of spectral types F0 through M5 are tabulated, and correlations examined with respect to the nature of their circumstellar envelopes. One-fourth of these objects were spatialy resolved by IRAS at 60 microns and possess extended circumstellar shell material, with implied expansion ages of about 10 to the 5th yr. Inferences about the production of dust, mass loss, and the relation of these characteristics of the evolution of massive stars, are discussed.

Stencel, Robert E.; Pesce, Joseph E.; Bauer, Wendy Hagen

1989-01-01

359

Trace Constituents, and the Habitability of Mars  

NASA Astrophysics Data System (ADS)

The only organic constituent ever reported on Mars is methane gas in the atmosphere. No organics -- indigenous or extraplanetary -- have ever been positively identified in the surface. The reported ``detection'' of methane is tantalizing, but tentative [1]. If confirmed, it would have important implications for extinct or extant life on Mars. Although life as we know it produces methane -- 90-95% of the methane in Earth's atmosphere is ultimately derived from biological processes -- the presence of methane at Mars does not necessarily imply existence of life, now or in the past. A precise knowledge of related trace constituents and stable isotopes in the atmosphere and solid samples, together with the geochemical and geologic data for determining preservation potential of the environment is essential to satisfactorily address the question of habitability of Mars. In this talk, we will review the current status of methane, related trace constituents and relevant isotopes, surface and atmospheric oxidants, and provide a brief summary of specific measurements planned by the Sample Analysis at Mars Investigation [2] on Mars Science Laboratory that are anticipated to make significant contribution to an understanding of habitability of Mars. Relevant publications may be downloaded from www.umich.edu/˜atreya. References: [1] S. K. Atreya, O. Witasse, V. F. Chevrier, F. Forget, P. R. Mahaffy, B. Price, C. R. Webster, R. W. Zurek, Methane on Mars: Current Observations, Interpretation, and Future Plans. Planet. Space Science, 59, 133-136, 2011, doi: 10.1016/j.pss.2010.10.008. [2] P. R. Mahaffy et al., The Sample Analysis at Mars Investigation and Instrument Suite on Mars Science Laboratory. Space Science Reviews, in press, 2012.

Atreya, Sushil K.; Mahaffy, Paul

2012-07-01

360

5FOOD HABITS OF TWO SOUTH AMERICAN CANIDS Food habits of two syntopic canids, the maned wolf (Chrysocyon  

E-print Network

5FOOD HABITS OF TWO SOUTH AMERICAN CANIDS Food habits of two syntopic canids, the maned wolf Paulo, 05508-900, Brasil; e-mail: abueno@ib.usp.br ABSTRACT The maned wolf (Chrysocyon brachyurus ingested mainly animal food if biomass is considered. The maned wolf consumed more wolf's fruit (Solanum

Motta Junior, Jose Carlos

361

Investigating Socioscientific Issues via Scientific Habits of Mind: Development and Validation of the Scientific Habits of Mind Survey  

ERIC Educational Resources Information Center

In this paper, we describe the Scientific Habits of Mind Survey (SHOMS) developed to explore public, science teachers' and scientists' understanding of habits of mind (HoM). The instrument contained 59 items, and captures the seven SHOM identified by Gauld. The SHOM was validated by administration to two cohorts of pre-service science teachers:…

Calik, Muammer; Coll, Richard Kevin

2012-01-01

362

Support for Florida Saves Provided Establish the habit of saving moneyEstablish the habit of saving money  

E-print Network

Support for Florida Saves Provided by #12; Establish the habit of saving moneyEstablish the habit of saving money Give yourself a raise every 3 monthsGive yourself a raise every 3 months Increase how much the money directly deposited into yourthe money directly deposited into your savings account.savings account

Jawitz, James W.

363

Applying behavior analysis to clinical problems: review and analysis of habit reversal.  

PubMed Central

This article provides a review and analysis of habit reversal, a multicomponent procedure developed by Azrin and Nunn (1973, 1974) for the treatment of nervous habits, tics, and stuttering. The article starts with a discussion of the behaviors treated with habit reversal, behavioral covariation among habits, and functional analysis and assessment of habits. Research on habit reversal and simplified versions of the procedure is then described. Next the article discusses the limitations of habit reversal and the evidence for its generality. The article concludes with an analysis of the behavioral processes involved in habit reversal and suggestions for future research. PMID:9757583

Miltenberger, R G; Fuqua, R W; Woods, D W

1998-01-01

364

Radiological Habits Survey: Dounreay, 2008 This page has been intentionally left blank  

E-print Network

Radiological Habits Survey: Dounreay, 2008 #12;This page has been intentionally left blank #12;Radiological Habits Survey: Dounreay, 2008 Final report The Centre for Environment, Fisheries & Aquaculture

365

Radiological Habits Survey: Hunterston, 2007 This page has been intentionally left blank  

E-print Network

Radiological Habits Survey: Hunterston, 2007 #12;This page has been intentionally left blank #12;Radiological Habits Survey: Hunterston, 2007 FINAL REPORT The Centre for Environment, Fisheries & Aquaculture

366

Temperate Oceans : Light Zones  

NSDL National Science Digital Library

This reference provides an overview of the three zones into which the ocean can be divided based on the amount of light recieved: the sunlit (or euphotic) zone, the twilight (or disphotic) zone, and the midnight (or aphotic) zone. The descriptions are accompanied by diagrams and a brief listing of the organisms that live in each zone.

2007-12-12

367

Can the interior structure influence the habitability of a rocky planet?  

NASA Astrophysics Data System (ADS)

Motivation: The most likely places for finding life outside the Solar System are rocky planets, some of which may have surface conditions allowing for liquid water, one of the major prerequisites for life. Greenhouse gases, such as carbon dioxide (CO2), play an important role for the surface temperature and, thus, the habitability of an extrasolar planet. The amount of greenhouse gases in the atmosphere is in part determined by their outgassing from the interior. Method: We use a two-dimensional convection model to calculate partial melting and the amount of CO2 outgassed for Earth-sized stagnant-lid planets. By varying the planetary mass, we investigate the evolution of a secondary atmosphere dependent on the interior structure (different ratio of planetary to core radius). We further study the likelihood for plate tectonics depending on the interior structure and investigate the influence of plate tectonics on outgassing. Results: We find that for stagnant-lid planets the relative size of the iron core has a large impact on the production of partial melt because a variation in the interior structure changes the pressure gradient and thereby the melting temperature of silicate rocks with depth. As a consequence, for planets with a large core (a radius of at least 70-75% of the planet?s radius), outgassing from the interior is strongly reduced in comparison to a planet with the same radius but a small core. This finding suggests that the outer edge of the habitable zone of a star not only depends on the distance from the star and thus the solar influx but also is further limited by small outgassing for stagnant-lid planets with a high average density, indicating a high iron content (e.g. Mercury and the recently detected exoplanets Kepler-10b and CoRoT-7b). This contradicts previous models that have assumed CO2 reservoirs being in principle unlimited for all planets. If plate tectonics is initiated, several tens of bars of CO2 can be outgassed in a short period of time - even for planets with a large iron core - and the outer boundary of the habitable zone is not influenced by the interior structure. It is, however, more difficult for planets with a thin mantle (in our test case, with a thickness of 10% of the planet?s radius) to initiate plate tectonics. Our results indicate that the interior structure may strongly influence the amount of CO2 in planetary atmospheres and, thereby, the habitability of rocky planets. To obtain better constraints on the interior structure accurate measurements of size and mass are necessary.

Noack, L.; Godolt, M.; von Paris, P.; Plesa, A.-C.; Stracke, B.; Breuer, D.; Rauer, H.

2014-08-01

368

Shocks throughout the circumstellar envelope of yellow hypergiant IRC+10420  

NASA Astrophysics Data System (ADS)

IRC+10420 is a yellow hypergiant, a massive and very luminous star believed to be evolving from the red supergiant towards the luminous blue variable or Wolf-Rayet phase. Previous interferometric observations reveal a very extended expanding molecular envelope (~20000 AU) traced not only in CO but, surprisingly, also in SiO. Because SiO is expected to condense onto dust grains at radii <200 AU in the envelopes of evolved stars, and the inferred bulk density of the envelope around IRC+10420 as traced in CO drops below the critical density (~10^5 cm^-3) necessary to strongly excite SiO at radii >4000 AU, the SiO envelope is expected to be relatively compact. Shocks in the outflowing molecular gas has been proposed to evaporate SiO from dust grains and also enhance the gas density locally thus giving rise to strong SiO emission. To deduce the local gas density and relative SiO abundance necessary to produce the observed SiO emission, we have observed IRC+10420 in SiO (1-0) with the EVLA to complement previously published observations in SiO (2-1) with the IRAM PdBI. Both these observations reveal a brightened SiO shell at a radius of ~6000-10000 AU, located just beyond a CO shell at a radius of ~5000 AU. Beyond this shell, the SiO emission decreases more steeply in brightness than the CO emission, and is detectable out to a radius of ~30000 AU. Through sophisticated radiative transfer modelling to reproduce the measured brightness temperature and line ratio in SiO (2-1)/SiO (1-0), we find that the local gas density required to excite SiO is ~10^(5-6) cm^-3 for radii <15000 AU, about an order of magnitude higher than the bulk gas density traced in CO, and ~10^(4-5) cm^-3 at larger radii to the outer detectable extent of the SiO envelope, again at least an order of magnitude higher than the bulk gas density traced in CO. The relative SiO abundance peaks at ~10^-6 at the abovementioned shell, decreasing to values of ~10^-7 within and ~10^-8 to ~10^-7 beyond this shell. For comparison, the typical SiO abundance around AGB stars is 10^-6 at radii of a few hundreds AU, and decreases steeply beyond. We attribute the enhanced SiO abundance in the shell relative to regions within and beyond to shocks between two mass-ejection episodes. As for the lower but still enhanced SiO abundance further out, we appeal to observations with the Hubble Space Telescope that show a multitude of knots distributed throughout (out to a projected distance of at least 10000 AU) and moving at relatively high velocities (~100 km/s) through the circumstellar envelope (expanding at a bulk velocity of ~40 km/s of IRC+10420. We speculate that shocks created by the motion of these knots relative to the gaseous envelope releases SiO, and that the enhanced density of these knots and/or gas compressed by the shocks excites SiO to produce the strong emission observed.

Wong, Ka-Tat; Lim, Jeremy; Dinh-V-Trung

2013-06-01

369

Water Masers in the Circumstellar Environments of Young Stellar Leb'ee S. G. Meehan  

E-print Network

Water Masers in the Circumstellar Environments of Young Stellar Objects Leb'ee S. G. Meehan with known water maser emission: RNO15FIR, Orion A­W, L1157, B361, and L1251A. These objects are cold IRAS their relationship to the water masers and tracers of their stellar winds. Compact radio continuum emission

Wilking, Bruce A.

370

DIFFERENTIAL PROPER-MOTION STUDY OF THE CIRCUMSTELLAR DUST SHELL OF THE ENIGMATIC OBJECT, HD 179821  

SciTech Connect

HD 179821 is an enigmatic evolved star that possesses characteristics of both a post-asymptotic giant branch (post-AGB) star and a yellow hypergiant, and there has been no evidence that unambiguously defines its nature. These two hypotheses are products of an indeterminate distance, presumed to be 1 kpc or 6 kpc. We have obtained the two-epoch Hubble Space Telescope Wild Field Planetary Camera 2 data of its circumstellar shell, which shows multiple concentric arcs extending out to about 8''. We have performed differential proper-motion measurements on distinct structures within the circumstellar shell of this mysterious star in hopes of determining the distance to the object, and thereby distinguishing the nature of this enigmatic stellar source. Upon investigation, rather than azimuthal radially symmetric expansion, we discovered a bulk motion of the circumstellar shell of (2.41 +- 0.43, 2.97 +- 0.32) mas yr{sup -1}. This corresponded to a translational interstellar medium (ISM) flow of (1.28 +- 0.95, 7.27 +- 0.75) mas yr{sup -1} local to the star. This finding implies that the distance to HD 179821 should be rather small in order for its circumstellar shell to preserve its highly intact spherical structure in the presence of the distorting ISM flow, therefore favoring the proposition that HD 179821 is a post-AGB object.

Ferguson, Brian A.; Ueta, Toshiya, E-mail: bferg@stsci.ed [Department of Physics and Astronomy, University of Denver, Denver, CO 80208 (United States)

2010-03-10

371

The circumstellar environment of the B[e] star GG Car: an interferometric modeling  

NASA Astrophysics Data System (ADS)

The research of stars with the B[e] phenomenon is still in its infancy, with several unanswered questions. Physically realistic models that treat the formation and evolution of their complex circumstellar environments are rare. The code HDUST (developed by A. C. Carciofi and J. Bjorkman) is one of the few existing codes that provides a self-consistent treatment of the radiative transfer in a gaseous and dusty circumstellar environment seen around B[e] supergiant stars. In this work we used the HDUST code to study the circumstellar medium of the binary system GG Car, where the primary component is probably an evolved B[e] supergiant. This system also presents a disk (probably circumbinary), which is responsible for the molecular and dusty signatures seen in GG Car spectra. We obtained VLTI/MIDI data on GG~Car at eight baselines, which allowed to spatially resolve the gaseous and dusty circumstellar environment. From the interferometric visibilities and SED modeling with HDUST, we confirm the presence of a compact ring, where the hot dust lies. We also show that large grains can reproduce the lack of structure in the SED and visibilities across the silicate band. We conclude the dust condensation site is much closer to the star than previously thought. This result provides stringent constraints on future theories of grain formation and growth around hot stars.

de Souza, A. Domiciano; Fernandes, M. Borges; Carciofi, A. C.; Chesneau, O.

2015-01-01

372

The upper intertidal zone  

NSDL National Science Digital Library

The upper intertidal zone is exposed most of the time and will become submerged only during high tide. This zone is least abundant of the intertidal zones but contains some mollusks, barnacles, and other animals adapted to avoid drying out.

Katie Hale (California State University, Fullerton; Student, Biological Sciences)

2007-01-04

373

The upper intertidal zone  

NSDL National Science Digital Library

The upper intertidal zone is exposed most of the time and will become submerged only during high tide. This zone is least abundant of the intertidal zones but contains some mollusks, barnacles, and other animals adapted to avoid drying out.

Katie Hale (CSUF; Biological Sciences)

2007-06-08

374

The bottom intertidal zone  

NSDL National Science Digital Library

The bottom intertidal area remains under water except during low tides. This zone is most abundant of the intertidal zones and contains seaweeds and other plants, invertebrates, and fishes. The bottom zone is subject to the most intense wave action.

Katie Hale (California State University, Fullerton; Student, Biological Sciences)

2007-01-04

375

The bottom intertidal zone  

NSDL National Science Digital Library

The bottom intertidal area remains under water except during low tides. This zone is most abundant of the intertidal zones and contains seaweeds and other plants, invertebrates, and fishes. The bottom zone is subject to the most intense wave action.

Katie Hale (CSUF; Biological Sciences)

2007-06-08

376

The circumstellar nature of the metallic features in a hot DA white dwarf  

NASA Technical Reports Server (NTRS)

A new co-added IUE echelle spectrum of the bright DA white dwarf CD -38 deg 10980, together with a newly determined radial velocity for this star, indicate that the sharp lined Si and C absorption features seen in the UV are clearly circumstellar in origin. Absorption in both excited and ground state transitions occurs at a velocity displaced by -12.1 +/- 2.0 km.s with respect to the photospheric velocity. Weak features due to the Si IV doublet are seen at a velocity intermediate between that of the circumstellar features and the photosphere. First time estimates of column densities for excited and ground states of C II, Si II, and Si III are derived. These quantities are used with electron density estimates derived from these species to determine the location and physical conditions of the circumstellar gas in the vicinity of CD -38 deg 10980. If collisional excitation alone is responsible for the excited levels of Si III observed in CD -38 deg 10980, then electron densities in the circumstellar gas must exceed 10(exp 9)/cu cm. Substantially lower electron densities are possible if the circumstellar gas is located near enough to the star so that photoexcitation is the dominant process responsible for the excited lines seen in the UV. Strong limits are placed on the photospheric abundance of Si and C in the star itself. These limits are in sharp contrast to the theoretical predictions of radiative levitation in which Si, but not C, is expected in the photosphere of a white dwarf such as CD -38 deg 10980. The interstellar line of sight to CD -38 deg 10980 is also investigated.

Holberg, J. B.; Bruhweiler, F. C.; Andersen, J.

1995-01-01

377

Dietary habits of athletes in Bahrain.  

PubMed

This study describes the dietary habits of athletes involved in four common sports in Bahrain (football, handball, volleyball and basketball). A sample of 304 athletes was obtained from 14 first class clubs. It was found that 28% of athletes skipped breakfast, and only 39% consumed breakfast daily. Foods eaten before competition were similar to those consumed by other family members, indicating that athletes did not eat any specific diet before events. There were some differences in meal patterns among athletes of various sports. In general, athletes allowed enough time between a meal and competition (2.8-3.1 hours). About half of them consumed water only at restbreak, while the rest consumed fruit drinks, tea and oranges in addition to water. Some (3%) did not consume any fluid. A small proportion of the athletes (4%) used vitamins and protein supplements. Mass media (53.6%) and coaches (20.1%) were the primary sources of nutrition information for athletes. It is suggested that information on nutrition and physical performance should be introduced in all educational programmes for both athletes and coaches. PMID:7761044

Musaiger, A O; Ragheb, M A

1994-01-01

378

Habitability & Astrobiology Research in Mars Terrestrial Analogues  

NASA Astrophysics Data System (ADS)

We performed a series of field research campaigns (ILEWG EuroMoonMars) in the extreme Utah desert relevant to Mars environments, and in order to help in the interpretation of Mars missions measurements from orbit (MEX, MRO) or from the surface (MER, MSL), or Moon geochemistry (SMART-1, LRO). We shall give an update on the sample analysis in the context of habitability and astrobiology. Methods & Results: In the frame of ILEWG EuroMoonMars campaigns (2009 to 2013) we deployed at Mars Desert Research station, near Hanksville Utah, a suite of instruments and techniques [A, 1, 2, 9-11] including sample collection, context imaging from remote to local and microscale, drilling, spectrometers and life sensors. We analyzed how geological and geochemical evolution affected local parameters (mineralogy, organics content, environment variations) and the habitability and signature of organics and biota. Among the important findings are the diversity in the composition of soil samples even when collected in close proximity, the low abundances of detectable PAHs and amino acids and the presence of biota of all three domains of life with significant heterogeneity. An extraordinary variety of putative extremophiles was observed [3,4,9]. A dominant factor seems to be soil porosity and lower clay-sized particle content [6-8]. A protocol was developed for sterile sampling, contamination issues, and the diagnostics of biodiversity via PCR and DGGE analysis in soils and rocks samples [10, 11]. We compare the 2009 campaign results [1-9] to new measurements from 2010-2013 campaigns [10-12] relevant to: comparison between remote sensing and in-situ measurements; the study of minerals; the detection of organics and signs of life. Keywords: field analogue research, astrobiology, habitability, life detection, Earth-Moon-Mars, organics References [A] Foing, Stoker & Ehrenfreund (Editors, 2011) "Astrobiology field Research in Moon/Mars Analogue Environments", Special Issue of International Journal of Astrobiology , IJA 2011, 10, vol. 3. 137-305 [1] Foing B. et al. (2011) Field astrobiology research at Moon-Mars analogue site: Instruments and methods, IJA 2011, 10 (3), 141;[2] Clarke, J., Stoker, C. Concretions in exhumed & inverted channels near Hanksville Utah: implications for Mars, (IJA 2011, 10 (3), 162;[3] Thiel et al., (2011) PCR-based analysis of microbial communities during the EuroGeoMars campaign at Mars Desert Research Station, Utah. (IJA 2011, 10 (3), 177;[4] Direito et al. (2011). A wide variety of putative extremophiles and large beta-diversity at the Mars Desert Research Station (Utah). (IJA 2011, 10 (3), 191;[5] Orzechowska, G. et al (20110 analysis of Mars Analog soils using solid Phase Microextraction, Organics solvent extraction and GCMS, (IJA 2011, 10 (3), 209; [6] Kotler et al. (2011). Analysis of mineral matrices of planetary soils analogs from the Utah Desert. (IJA 2011, 10 (3), 221; [7] Martins et al. (2011). Extraction of amino acids from soils close to the Mars Desert Research Station (MDRS), Utah. (IJA 2011, 10 (3), 231; [8] Ehrenfreund et al. (2011) Astrobiology and habitability studies in preparation for future Mars missions: trends from investigating minerals, organics and biota. (IJA 2011, 10 (3), 239; [9] Stoker C. et al (2011) Mineralogical, Chemical, Organic & Microbial Properties of Subsurface Soil Cores from Mars Desert Research Station, a Phyllosilicate and Sulfate Rich Mars Analog Site, IJA 2011, 10 (3), 269; [10] Rodrigues L. et al (2014, in preparation) Preventing biocontamination during sterile sampling; [11] Rodrigues L. et al (2014, in preparation) Microbial diversity in MDRS rocks and soils; [12] ILEWG EuroMoonMars Team, (2014, special issue in preparation) Results from ILEWG EuroMoonMars campaign 2013 **Acknowledgements: B.H.Foing (1, 2, 6), C. Stoker (3), P. Ehrenfreund (4, 5), I. Rammos (2), L. Rodrigues (2), A. Svendsen (2), D. Oltheten (2), K. Nebergall (6), M. Battler (6, 7), H. v't Houd (8), A. Bruneau (6,9), M. Cross (6,7), V. Maivald (10), C. Orgel (6), A. Elsaesser (4),

Foing, Bernard

2014-05-01

379

Food habits and preferences of Vietnamese children.  

PubMed

In this study, information on food preferences and intake frequencies of 70 Vietnamese children was gathered by means of a questionnaire. The purpose was to compare the dietary habits of children who had been in the U.S. for more than one year with those of children arriving within the past year (1981). The results showed that children less than six years old who came to California more than one year ago consumed green leafy vegetables less frequently (p less than 0.01) and vitamin supplements more frequently (p less than 0.01) than those who came here recently. In the older groups (greater than 6 yrs), those who have been resident in the U.S. for more than one year consumed peanut butter and sweets (ice cream, pies, milkshakes) more frequently than those who had just arrived (p less than 0.001 and p less than 0.05, respectively). Older children (age greater than 6 yrs) who had been in the U.S. longer preferred American foods more than those who had just come (p less than 0.01). The majority of all children ate fruits as snacks. The consumption of rice, eggs, cheese, milk, meats and fruit juice was not significantly different in any of the four groups. This study also revealed a great need of nutrition education for the Vietnamese refugee mothers. Recommendations for planning nutrition education for this population are provided. PMID:6550681

Thuy, T N; Tam, H D; Craig, W J; Zimmerman, G

1983-02-01

380

[Smoking habits among physicians in Dakar].  

PubMed

A prospective cross-sectional study was conducted in March 1999 on the prevalence of smokers and smoking habits among physicians practicing in the Dakar region. The study population was composed of 163 physicians; 128 male (78.5%) and 35 female (21.5%). The prevalence of smokers was 27.6%. The average age of the smokers was 40.5 (+/- 6.2) years (extremes between 30 and 61 years) and an average duration of 18 (+/- 6.6) years in smoking. Men smoked more than women (93.9% versus 6.7%) with 56.4% of heavy smokers. Specialists represented 63.3% and generalists 36.4%. Initiating factors were stress (28.9%), circle of friends/acquaintances (24.4%), fashion (24.4%), pleasure (20%) and advertisements (2.2%). A little over 82% smoked in public places, 68.9% in their work places and 49.5% before children. The average time duration smoking was stopped followed by relapse was 15.7 (+/- 9.7) months. 97.7% of smokers manifested their intention to stop. Nicotine dependence according too the Fagerström questionnaire was average (37.9%), high (39.6%) and very high (12.6%). Smoking is a reality in the medical environment in Dakar. Specific campaigns aimed at physicians will be necessary to hope for a sustainable change in behavior and for a much more pronounced implication in the fight against tobacco addiction. PMID:11373598

Ndiaye, M; Hane, A A; Ndir, M; Ba, O; Diop-Dia, D; Kandji, M; Ndiaye, S; Toure, N O; Diatta, A; Dia, Y; Niang, A; Wone, I; Sow, M L

2001-02-01

381

Red Optical Planet Survey: a new search for habitable earths in the southern sky  

NASA Astrophysics Data System (ADS)

We present the first results from our Red Optical Planet Survey to search for low-mass planets orbiting late-type dwarfs (M5.5V-M9V) in their habitable zones. Our observations with the red arm of the Magellan Inamori Kyocera Echelle spectrograph (0.5-0.9 ?m) at the 6.5-m Magellan Clay telescope at Las Campanas Observatory indicate that ?92 per cent of the flux lies beyond 0.7 ?m. We use a novel approach that is essentially a hybrid of the simultaneous iodine and ThAr methods for determining precision radial velocities. We apply least squares deconvolution to obtain a single high signal-to-noise ratio (S/N) stellar line for each spectrum and cross-correlate against the simultaneously observed telluric line profile, which we derive in the same way. Utilizing the 0.62-0.90 ?m region, we have achieved an rms precision of 10 ms-1 for an M5.5V spectral type star with spectral S/N ˜ 160 on 5-min time-scales. By M8V spectral type, a precision of ˜30 ms-1 at S/N = 25 is suggested, although more observations are needed. An assessment of our errors and scatter in the radial velocity points hints at the presence of stellar radial velocity variations. Of our sample of seven stars, two show radial velocity signals at 6? and 10? of the cross-correlation uncertainties. We find that chromospheric activity (via H? variation) does not have an impact on our measurements and are unable to determine a relationship between the derived photospheric line profile morphology and radial velocity variations without further observations. If the signals are planetary in origin, our findings are consistent with estimates of Neptune mass planets that predict a frequency of 13-27 per cent for early M dwarfs. Our current analysis indicates the we can achieve a sensitivity that is equivalent to the amplitude induced by a 6 M? planet orbiting in the habitable zone. Based on simulations, we estimate that <10 M? habitable zone planets will be detected in a new stellar mass regime, with ?20 epochs of observations. Higher resolution and greater instrument stability indicate that photon-limited precisions of 2 ms-1 are attainable on moderately rotating M dwarfs (with vsin i? 5 km s-1) using our technique.

Barnes, J. R.; Jenkins, J. S.; Jones, H. R. A.; Rojo, P.; Arriagada, P.; Jordán, A.; Minniti, D.; Tuomi, M.; Jeffers, S. V.; Pinfield, D.

2012-07-01

382

Functional Neuroimaging of Avoidance Habits in Obsessive-Compulsive Disorder  

E-print Network

Objective: The goal of this study was to determine the neural correlates of excessive habit formation in obsessive-compulsive disorder (OCD). We aimed to (i) test for neurobiological convergence with the known pathophysiology of OCD and (ii) infer...

Gillan, Claire M.; Apergis-Schoute, Annemieke M.; Morein-Zamir, Sharon; Urcelay, Gonzalo P.; Sule, Akeem; Fineberg, Naomi A.; Sahakian, Barbara J.; Robbins, Trevor W.

383

Skylab experiment M487 habitability/crew quarters  

NASA Technical Reports Server (NTRS)

Results of Skylab experiment M487 (habitability/crew quarters), which was designed to evaluate the habitability features of Skylab, were presented. General observations and conclusions drawn from the data obtained are presented in detail. The objectives of the experiment, the manner in which data was acquired, and the instruments used to support the experiments are described. Illustrations and photographs of the living and work areas of Skylab and some of the habitability features are provided. Samples of the subjective evaluation questionnaires used by the crewmen are included. Habitability-related documents, crewmen biographies, functional characteristics and photographs of the instruments used, and details of Skylab compartment sizes and color schemes are included as appendixes.

Johnson, C. C.

1975-01-01

384

Root Apex Transition Zone As Oscillatory Zone  

PubMed Central

Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and critical inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Here we discuss the oscillatory nature of the transition zone which, together with several other features of this zone, suggest that it acts as some kind of command center. In accordance with the early proposal of Charles and Francis Darwin, cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone. PMID:24106493

Baluška, František; Mancuso, Stefano

2013-01-01

385

Habits: bridging the gap between personhood and personal identity  

PubMed Central

In philosophy, the criteria for personhood (PH) at a specific point in time (synchronic), and the necessary and sufficient conditions of personal identity (PI) over time (diachronic) are traditionally separated. Hence, the transition between both timescales of a person's life remains largely unclear. Personal habits reflect a decision-making (DM) process that binds together synchronic and diachronic timescales. Despite the fact that the actualization of habits takes place synchronically, they presuppose, for the possibility of their generation, time in a diachronic sense. The acquisition of habits therefore rests upon PI over time; that is, the temporal extension of personal decisions is the necessary condition for the possible development of habits. Conceptually, habits can thus be seen as a bridge between synchronic and diachronic timescales of a person's life. In order to investigate the empirical mediation of this temporal linkage, we draw upon the neuronal mechanisms underlying DM; in particular on the distinction between internally and externally guided DM. Externally guided DM relies on external criteria at a specific point in time (synchronic); on a neural level, this has been associated with lateral frontal and parietal brain regions. In contrast, internally guided DM is based on the person's own preferences that involve a more longitudinal and thus diachronic timescale, which has been associated with the brain's intrinsic activity. Habits can be considered to reflect a balance between internally and externally guided DM, which implicates a particular temporal balance between diachronic and synchronic elements, thus linking two different timescales. Based on such evidence, we suggest a habit-based neurophilosophical approach of PH and PI by focusing on the empirically-based linkage between the synchronic and diachronic elements of habits. By doing so, we propose to link together what philosophically has been described and analyzed separately as PH and PI. PMID:24904370

Wagner, Nils-Frederic; Northoff, Georg

2014-01-01

386

Covey's seven habits and the systems approach: a comparative analysis  

Microsoft Academic Search

This paper advances the premise that the best seller book by Stephen Covey: The Seven Habits of Highly Effective People and the systems approach share common-principles and philosophy. Indeed, each of the seven habits-be proactive; begin with the end in mind; put first thing first; think win\\/win; seek first to understand, then to be understood; synergize; and sharpen the saw-is

Y. Y. Haimes; C. Schneiter

1996-01-01

387

Search for and study of hot circumstellar dust envelopes  

NASA Astrophysics Data System (ADS)

Long-term (1984-2008) JHKLM photometry for 254 objects is presented. The observations were carried out in the standard JHKLM photometric system using an original method and a modern IR photometer designed and built at the Sternberg Astronomical Institute. Our program of studies included searches for and studies of relatively hot circumstellar dust envelopes. The most important results obtained using these observations include the following. We have detected relatively hot dust envelopes in a number of objects for the first time, including the RCB star UV Cas, RX Cas, several classical symbiotic stars, etc. A model has been calculated for the dust envelope of FG Sge, which formed around the star as a result of several successive cycles of dust condensation beginning in Autumn 1992. Several dust-condensation episodes have been traced in the envelopes of symbiotic systems (CH Cyg, V1016 Cyg, HM Sge, etc.), as well as the role of the hot component in the formation of the dust envelopes. We have established from variations of the IR emission that the cool components in the symbiotic novae V1016 Cyg and HM Sge, and possibly CH Cyg, are Miras. The binarity of V1016 Cyg and HM Sge has also been firmly established. The variability of a whole series of object has been studied, including the stellar components of close binary systems and several dozen Mira and semi-regular variables. The ellipsoidality of the components in the RX Cas system (a prototype W Ser star) and the cool component in the symbiotic systems CI Cyg and BF Cyg has been firmly established. We have obtained the first IR light curve for the eclipsing system V444 Cyg (WN5+O6), and determined the wavelength dependence of the obtained parameters of the WN5 star. Analysis of the IR light curves of several novae indicate the condensation of dust envelopes in the transition periods of Cygnus 1992, Aquila 1993, and Aquila 1995. The IR light curve of R CrB has been obtained over a long period and analyzed. IR observations of the nova-like variable V4334 Sgr have been carried out over four years, over which the star passed through four stages during its motion along its post-AGB evolutionary track; the star's bolometric flux and optical depth of its dust envelope have been estimated, and the structure and mass of the dust layer determined. We have analyzed the IR variability of the symbiotic star V407 Cyg over 14 years, and found its cool component to be a Mira with a period of 745 days. The observed pulsations and trend are associated with the luminosity and temperature variations of the Mira, as well as the optical depth of the dust envelope. The size of the dust grains and mass-loss rate of the Mira have been determined. We have obtained JHKL light curves for the Seyfert galaxy NGC 4151 over 23 years. The IR brightness of the galaxy grew from 1985 through 1996 (by ˜0.9 m at 1.25 µm, ˜1 m at 1.65 µm, ˜1.1 m at 2.2 µm, and ˜1.3 m at 3.5 µm), while the galaxy simultaneously reddened. The "cool" variable source in NGC 4151 was still in the active state in 1998, although its luminosity had decreased by approximately 15%-20%. If the "cool" component of the variable source in this galaxy is a dust envelope heated by the central "hot" source, it should be optically thin to the radiation of this source: its mean optical depth is in the range 0.05-0.15. Emission from dust particles heated to temperatures of 600-800 K was observed in the near IR at a distance of several parsecs from the nucleus during the period of activity in 1995-1998; the inferred mass of emitting dust was 5-20 M ?. In 1994-2003, we observed a tendency for NGC 4151 to become bluer at 1.25-1.65 µm while simultaneously reddening at 2.2-3.5 µm. Beginning in Autumn 2000, the galaxy began to emerge from a minimum, which lasted from March 2000 through April 2001 in the IR; a flare of the galactic nucleus was observed and followed in detail in the IR in this same period. We confirm the IR variability of the nucleus of the Seyfert galaxy NGC 1068, which can be located in various

Shenavrin, V. I.; Taranova, O. G.; Nadzhip, A. E.

2011-01-01

388

Theoretical studies of the infrared emission from circumstellar dust shells - The infrared characteristics of circumstellar silicates and the mass-loss rate of oxygen-rich late-type giants  

NASA Technical Reports Server (NTRS)

A simple analytic formula and a numerical radiative transfer program have been used to model the IR emission of spherically symmetric circumstellar dust shells in order to determine the IR absorption properties of circumstellar silicate grains and the mass-loss rates of the central stars. The correlation between the near-IR color temperature and the strength of the 10-micron emission or absorption feature is discussed, and it is shown that the near-IR absorption efficiency of circumstellar silicate grains is much higher than is expected from terrestrial minerals, possibly due to the presence of Fe(2+) color centers dissolved in the circumstellar silicates. Detailed models of the IR emission of R Cas, IRC 10011, and OH 26.5+0.6 are presented.

Schutte, W. A.; Tielens, A. G. G. M.

1989-01-01

389

Numerical quantification of habitability in serpentinizing systems  

NASA Astrophysics Data System (ADS)

The likely presence of liquid water in contact with olivine-bearing rocks on Mars, the detection of serpentine minerals and of methane emissions possibly consistent with serpentinization, and the observation of serpentine-associated methane-cycling communities on Earth have all led to excitement over the potential of such systems to host life on Mars, even into the present day. However, the habitability of subsurface serpentinizing systems on Mars does not necessarily follow from these qualitative observations. In particular, while the production of H2 during serpentinization could provide methanogens with a needed substrate, the alkaline conditions and corresponding potential for carbon limitation that arise in concert are negatives against which H2 supply must be balanced. We considered this balance via a coupled geochemical-bioenergetic model that weighs the outputs of serpentinization against the metabolic requirements of methanogenesis, in an energetic frame of reference. Serpentinization is modeled using the "Geochemist's Workbench" (GWB) whereby ultramafic harzburgite rocks are reacted with oxygen and sulfate depleted seawater. Reaction kinetics are not explicitly considered, but comparable effects of partial reaction are approximated by assuming post-reaction dilution of equilibrated fluids. The output of GWB serves as the input to the bioenergetic model, which calculates methanogenic energy yields based on spherically-symmetrical diffusion of substrates to a cell followed by reaction at the diffusion-limited rate. Membrane selectivity for substrate transport is explicitly considered. Results will be report updates for two scenarios: (i) High temperature serpentinization followed by cooling and transport of equilibrated fluid to a lower temperature regime accessible to biology; (ii) Serpentinization within the biologically-tolerated range of temperatures. Such coupled models demonstrate that environmental variability with respect to both water-rock reaction, temperature, and biologically-mediated methanogenesis drive orders of magnitude variability in the energy available in methanogenic metabolism.

Som, S.; Alperin, M. J.; Hoehler, T. M.

2012-12-01

390

Microbial habitability of the Hadean Earth during the late heavy bombardment.  

PubMed

Lunar rocks and impact melts, lunar and asteroidal meteorites, and an ancient martian meteorite record thermal metamorphic events with ages that group around and/or do not exceed 3.9 Gyr. That such a diverse suite of solar system materials share this feature is interpreted to be the result of a post-primary-accretion cataclysmic spike in the number of impacts commonly referred to as the late heavy bombardment (LHB). Despite its obvious significance to the preservation of crust and the survivability of an emergent biosphere, the thermal effects of this bombardment on the young Earth remain poorly constrained. Here we report numerical models constructed to probe the degree of thermal metamorphism in the crust in the effort to recreate the effect of the LHB on the Earth as a whole; outputs were used to assess habitable volumes of crust for a possible near-surface and subsurface primordial microbial biosphere. Our analysis shows that there is no plausible situation in which the habitable zone was fully sterilized on Earth, at least since the termination of primary accretion of the planets and the postulated impact origin of the Moon. Our results explain the root location of hyperthermophilic bacteria in the phylogenetic tree for 16S small-subunit ribosomal RNA, and bode well for the persistence of microbial biospheres even on planetary bodies strongly reworked by impacts. PMID:19458721

Abramov, Oleg; Mojzsis, Stephen J

2009-05-21

391

Climate of Earth-like planets with high obliquity and eccentric orbits: Implications for habitability conditions  

NASA Astrophysics Data System (ADS)

We explore the effects of seasonal variability for the climate of Earth-like planets as determined by the two parameters polar obliquity and orbital eccentricity using a general circulation model of intermediate complexity. In the first part of the paper we examine the consequences of different values of obliquity and eccentricity for the spatio-temporal patterns of radiation and surface temperatures as well as for the main characteristics of the atmospheric circulation. In the second part of the paper we analyse the associated implications for the habitability of planets close to the outer edge of the habitable zone (HZ). The second part focuses in particular on the multistability property of climate, i.e. the parallel existence of both an ice-free and an ice-covered climate state. Our results show that seasonal variability affects both the existence of and transitions between the two climate states. Moreover, our experiments reveal that planets with Earth-like atmospheres and high seasonal variability can have ice-free areas at much larger distance from the host star than planets without seasonal variability, which leads to a substantial expansion of the outer edge of the HZ. Sensitivity experiments exploring the role of azimuthal obliquity and surface heat capacity test the robustness of our results. On circular orbits, our findings obtained with a general circulation model agree well with previous studies based on one dimensional energy balance models, whereas significant differences are found on eccentric orbits.

Linsenmeier, Manuel; Pascale, Salvatore; Lucarini, Valerio

2015-01-01

392

Detecting "Temperate" Jupiters: The Prospects of Searching for Transiting Gas Giants in Habitability Zones  

E-print Network

This paper investigates the effects of observing windows on detecting transiting planets by calculating the fraction of planets with a given period that have zero, one (single), two (double), or $\\ge$3 (multiple) transits occurring while observations are being taken. We also investigate the effects of collaboration by performing the same calculations with combined observing times from two wide-field transit survey groups. For a representative field of the 2004 observing season, both XO and SuperWASP experienced an increase in single and double transit events by up to 20-40% for planets with periods 14 planets with periods 14-150 days should have been observed at least once. For the SuperWASP Project, 50-90% of planets with periods between 14-150 days should have been observed at least once. If XO and SuperWASP combined their observations, 50-100% of planets with periods less than 20 days should be observed three or more times. We find that in general wide-field transit surveys have selected appropriate observing strategies to observe a significant fraction of transiting giant planets with semimajor axes larger than the Hot Jupiter regime. The actual number of intermediate-period transiting planets that are detected depends upon their true semimajor axis distribution and the signal-to-noise of the data.

S. W. Fleming; S. R. Kane; P. R. McCullough; F. R. Chromey

2008-02-18

393

High precision astrometry mission for the detection and characterization of nearby habitable planetary systems with the Nearby Earth Astrometric Telescope (NEAT)  

Microsoft Academic Search

A complete census of planetary systems around a volume-limited sample of solar-type stars (FGK dwarfs) in the Solar neighborhood (d <= 15 pc) with uniform sensitivity down to Earth-mass planets within their Habitable Zones out to several AUs would be a major milestone in extrasolar planets astrophysics. This fundamental goal can be achieved with a mission concept such as NEAT---the

Fabien Malbet; Alain Léger; Michael Shao; Renaud Goullioud; Pierre-Olivier Lagage; Anthony G. A. Brown; Christophe Cara; Gilles Durand; Carlos Eiroa; Philippe Feautrier; Björn Jakobsson; Emmanuel Hinglais; Lisa Kaltenegger; Lucas Labadie; Anne-Marie Lagrange; Jacques Laskar; René Liseau; Jonathan Lunine; Jesús Maldonado; Manuel Mercier; Christoph Mordasini; Didier Queloz; Andreas Quirrenbach; Alessandro Sozzetti; Wesley Traub; Olivier Absil; Yann Alibert; Alexandre Humberto Andrei; Frédéric Arenou; Charles Beichman; Alain Chelli; Charles S. Cockell; Gilles Duvert; Thierry Forveille; Paulo J. V. Garcia; David Hobbs; Alberto Krone-Martins; Helmut Lammer; Nadège Meunier; Stefano Minardi; André Moitinho de Almeida; Nicolas Rambaux; Sean Raymond; Huub J. A. Röttgering; Johannes Sahlmann; Peter A. Schuller; Damien Ségransan; Franck Selsis; Jean Surdej; Eva Villaver; Glenn J. White; Hans Zinnecker

2011-01-01

394

Habitability in different Milky Way stellar environments: a stellar interaction dynamical approach.  

PubMed

Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the solar neighborhood, however, is rather poor; thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 10(8) yr. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments. PMID:23659647

Jiménez-Torres, Juan J; Pichardo, Bárbara; Lake, George; Segura, Antígona

2013-05-01

395

Habitability In Close Binary Systems: Conditions For An Earth-Analogue  

NASA Astrophysics Data System (ADS)

Thanks to the Kepler telescope, and other efforts, the number of known exoplanets has dramatically increased. Detections include planets in binary star systems. The presence of a planet in the habitable zone of a star, or a binary star, is a necessary but not sufficient condition for complex life; which may be quite restrictive, e.g. Ward and Brownlee (2000). Some factors that may make life rare are specific to the planet including the right mass, composition, rotation rate, eccentricity, and axial tilt. Others may be thought of as external factors: intensity and spectrum of stellar radiation, presence in a suitable region of the galaxy, and a stabilizing tidal force. Especially important Earth-Analogue factors appear to include the need for a strong tidal effect and the grand paradox of water in the habitable zone. We generate an ensemble of Earth-analogue planets in P-type close binaries, using random stellar masses, binary semi-major axis, and binary eccentricity. Binaries are selected that provide both a minimally varying radiation flux and a time averaged tidal force, in the HZ, similar to Earth’s. When the flux variability is restricted to no more than 6 percent, solutions are found reproducing the time averaged tidal force experienced by Earth. The binaries that met these requirements had a mass ratio greater than 0.8. The ideal minimum flux variability solution is a pair of (nearly) identical early-K stars (near 4900 K) in a circular orbit with a = 0.045 AU, and a planet at 0.93 AU. Next we determine if the time dependent tidal force the Earth experiences can be approximated. These solutions involve binary eccentricities near 0.4 and significant flux variability. We argue that the long life-times of K-stars, and low UV radiation, may provide a niche for complex life.

Mason, Paul A.; Clark, J. M.

2012-05-01

396

Circumstellar dust shells around long-period variables. X. Dynamics of envelopes around standard luminous, C-rich AGB stars  

NASA Astrophysics Data System (ADS)

Context. Long-period variables (LPVs) and Miras exhibit a pronounced variability in their luminosity with a more or less well-defined period, and they suffer large mass loss in the form of stellar winds. Owing to this extensive mass loss, they are surrounded by extended circumstellar dust shells (CDSs). The dynamics of these envelopes is the result of a complex interplay via an external excitation by the pulsating central star, dust formation, and radiative transfer. Aims: Our study is aimed at an understanding of the dynamics of CDSs around carbon-rich, standard luminous LPVs and Miras. These shells often show multiperiodicity with secondary periods as high as a few 104 d superimposed on a main period that is in the range of approximately 102-103 d. Such secondary periods may be caused at least in part by the presence of dust. Methods: We consider an excitation of the CDSs either by a harmonic force, provided by the oscillation of the central star, or by a stochastic force with a continuous power spectrum. The resulting numerically computed dynamical behaviour of the shell is analysed with the help of Fourier analysis and stroboscopic maps. Results: CDSs may be described as multioscillatory systems that are driven by the pulsating stars. A set of normal modes can be identified. The obtained periods of these modes are some 103 d, which is a characteristic timescale for dust nucleation, growth, and elemental enrichment in the dust formation zone. Depending on the oscillation period and strength of the central star, the envelope reacts periodically, multi- periodically, or irregularly.

Dreyer, C.; Hegmann, M.; Sedlmayr, E.

2011-01-01

397

Effects of multiquantum transitions on molecular populations in grain-forming circumstellar environments  

NASA Technical Reports Server (NTRS)

Simplification of astrophysical calculations can be achieved by invoking the condition of local thermodynamic equilibrium; however, recent investigations suggest that this assumption may not be valid for certain astrophysical regions. To examine the effects of multiquantum translation to vibration transitions in expanding circumstellar envelopes, vibrational populations of the lowest 20 levels of CO have been calculated as a function of pressure and radiation density for H atom-CO collisions. Significant departure from local thermodynamic equilibrium is indicated, which implies lower dissociation rates for molecular components and a subsequent enhancement in the rate of grain formation by many orders of magnitude. Stabilization of intermediate species before they can dissociate may facilitate the formation of refractory grain cores in very hot, dilute outflows. As the present calculations indicate, laboratory measurements of state-to-state translation to vibration rates are needed for a more complete understanding of circumstellar chemistry.

Nuth, J. A.; Allen, J. E., Jr.; Wiant, M.

1985-01-01

398

Linear Polarization and the Dynamics of Circumstellar Disks of Classical Be Stars  

NASA Astrophysics Data System (ADS)

The intrinsic linearly polarized light arising from electron scattering of stellar radiation in a non-spherically symmetric distribution of gas is a characterizing feature of classical Be stars. The distinct polarimetric signature provides a mean for directly probing the physical and geometric properties of the gaseous material enveloping these rapidly-rotating massive stars. Using a Monte Carlo radiative transfer computation and a self-consistent radiative equilibrium solution for the circumstellar gas, we explore the role of this observable signature in investigating the dynamical nature of classical Be star disks. In particular, we focus on the potential for using linearly polarized light to develop diagnostics of mass-loss events and to trace the evolution of the gas in a circumstellar disk. An informed context for interpreting the observed linear polarization signature can play an important role in identifying the physical process(es) which govern the formation and dissipation of the gaseous disks surrounding classical Be stars.

Halonen, Robbie J.; Jones, Carol E.

2015-01-01

399

Limits on O VI Emission from the Shocked Circumstellar Gas of SN 1987A  

NASA Technical Reports Server (NTRS)

The Far Ultraviolet Spectroscopic Explorer (FUSE) was used to search for emission from the shock interaction of the ejecta of SN 1987A with its circumstellar material. FUSE observations of SN 1987A between 2000 and 2007 did not detect broad OVI emission. However, OVI emission was detected in 2000-2001 with a narrow line width (FWHM <35 kms t ) and a heliocentric radial velocity of +280 km/s. This places the emitting gas at rest relative to the supernova and is interpreted as emission from unshocked circumstellar gas. This narrow emission had disappeared in 2007 (and possibly earlier) as a result of the advancing shock overtaking the H II region that was flash ionized by the supernova explosion in 1987.

Sonneborn, George; Iping, Rosina C.; Fransson, Claes

2008-01-01

400

CHIC - Coupling Habitability, Interior and Crust  

NASA Astrophysics Data System (ADS)

We present a new code developed for simulating convection in terrestrial planets and icy moons. The code CHIC is written in Fortran and employs the finite volume method and finite difference method for solving energy, mass and momentum equations in either silicate or icy mantles. The code uses either Cartesian (2D and 3D box) or spherical coordinates (2D cylinder or annulus). It furthermore contains a 1D parametrised model to obtain temperature profiles in specific regions, for example in the iron core or in the silicate mantle (solving only the energy equation). The 2D/3D convection model uses the same input parameters as the 1D model, which allows for comparison of the different models and adaptation of the 1D model, if needed. The code has already been benchmarked for the following aspects: - viscosity-dependent rheology (Blankenbach et al., 1989) - pseudo-plastic deformation (Tosi et al., in preparation phase) - subduction mechanism and plastic deformation (Quinquis et al., in preparation phase) New features that are currently developed and benchmarked include: - compressibility (following King et al., 2009 and Leng and Zhong, 2008) - different melt modules (Plesa et al., in preparation phase) - freezing of an inner core (comparison with GAIA code, Huettig and Stemmer, 2008) - build-up of oceanic and continental crust (Noack et al., in preparation phase) The code represents a useful tool to couple the interior with the surface of a planet (e.g. via build-up and erosion of crust) and it's atmosphere (via outgassing on the one hand and subduction of hydrated crust and carbonates back into the mantle). It will be applied to investigate several factors that might influence the habitability of a terrestrial planet, and will also be used to simulate icy bodies with high-pressure ice phases. References: Blankenbach et al. (1989). A benchmark comparison for mantle convection codes. GJI 98, 23-38. Huettig and Stemmer (2008). Finite volume discretization for dynamic viscosities on Voronoi grids. PEPI 171(1-4), 137-146. King et al. (2009). A Community Benchmark for 2D Cartesian Compressible Convection in the Earth's Mantle. GJI 179, 1-11. Leng and Zhong (2008). Viscous heating, adiabatic heating and energetic consistency in compressible mantle convection. GJI 173, 693-702.

Noack, Lena; Labbe, Francois; Boiveau, Thomas; Rivoldini, Attilio; Van Hoolst, Tim

2014-05-01

401

Thermal--orbital coupled tidal heating and habitability of Martian-sized extrasolar planets around M stars  

E-print Network

M type stars are good targets in the search for habitable extrasolar planets. Because of their low effective temperatures, the habitable zone of M stars is very close to the star itself. For planets close to their stars, tidal heating plays an important role in thermal and orbital evolutions, especially when the planet orbit has a relatively large eccentricity. Although tidal heating interacts with the thermal state and orbit of the planet, such coupled calculations for extrasolar planets around M star have not been conducted. We perform coupled calculations using simple structural and orbital models, and analyze the thermal state and habitability of a terrestrial planet. Considering this planet to be Martian sized, the tide heats up and partially melts the mantle, maintaining an equilibrium state if the mass of the star is less than 0.2 times the mass of the Sun and the initial eccentricity of the orbit is more than 0.2. The reduction of heat dissipation due to the melted mantle allows the planet to stay in ...

Shoji, Daigo

2014-01-01

402

Evolution of a Subduction Zone  

NASA Astrophysics Data System (ADS)

The purpose of this study is to understand how Earth's surface might have evolved with time and to examine in a more general way the initiation and continuance of subduction zones and the possible formation of continents on an Earth-like planet. Plate tectonics and continents seem to influence the likelihood of a planet to harbour life, and both are strongly influenced by the planetary interior (e.g. mantle temperature and rheology) and surface conditions (e.g. stabilizing effect of continents, atmospheric temperature), but may also depend on the biosphere. Employing the Fortran convection code CHIC (developed at the Royal Observatory of Belgium), we simulate a subduction zone with a pre-defined weak zone (between oceanic and continental crust) and a fixed plate velocity for the subducting oceanic plate (Quinquis et al. in preparation). In our study we first investigate the main factors that influence the subduction process. We simulate the subduction of an oceanic plate beneath a continental plate (Noack et al., 2013). The crust is separated into an upper crust and a lower crust. We apply mixed Newtonian/non-Newtonian rheology and vary the parameters that are most likely to influence the subduction of the ocanic plate, as for example density of the crust/mantle, surface temperature, plate velocity and subduction angle. The second part of our study concentrates on the long-term evolution of a subduction zone. Even though we model only the upper mantle (until a depth of 670km), the subducted crust is allowed to flow into the lower mantle, where it is no longer subject to our investigation. This way we can model the subduction zone over long time spans, for which we assume a continuous inflow of the oceanic plate into the investigated domain. We include variations in mantle temperatures (via secular cooling and decay of radioactive heat sources) and dehydration of silicates (leading to stiffening of the material). We investigate how the mantle environment influences the subduction of the oceanic crust in terms of subduction velocity and subduction angle over time. We develop scaling laws combining the subduction velocity and angle depending on the mantle environment (and thus time). These laws can then be applied to continental growth simulations with 1D parameterized models (Höning et al., in press) or 2D/3D subduction zone simulations at specific geological times (using the correct subduction zone setting). References: Quinquis, M. et al. (in preparation). A comparison of thermo-mechanical subduction models. In preparation for G3. Noack, L., Van Hoolst, T., Dehant, V., and Breuer, D. (2013). Relevance of continents for habitability and self-consistent formation of continents on early Earth. XIII International Workshop on Modelling of Mantle and Lithosphere Dynamics, Hønefoss, Norway, 31. Aug. - 5. Sept. 2013. Höning, D., Hansen-Goos, H., Airo, A., and Spohn, T. (in press). Biotic vs. abiotic Earth: A model for mantle hydration and continental coverage. Planetary and Space Science.

Noack, Lena; Van Hoolst, Tim; Dehant, Veronique

2014-05-01

403

Toward Mapping the Detailed Density Structure of Classical Be Circumstellar Disks  

NASA Technical Reports Server (NTRS)

We present the preliminary results of near contemporaneous optical and infrared spectroscopic observations of select classical Be stars. We find strong evidence of oppositely oriented V/R hydrogen line profiles in the optical versus infrared spectra of zeta Tau, and briefly discuss how sustained contemporaneous optical and infrared spectroscopic observations might enable us to trace the detailed density structure of classical Be circumstellar disks.

Wisniewski, J. P.; Kowalski, A. F.; Bjorkman, K. S.; Bjorkman, J. E.

2005-01-01

404

Exocomets and variable circumstellar gas absorption in the debris disks of nearby A-type stars  

NASA Astrophysics Data System (ADS)

Over the past five years, more than a dozen new star systems have been discovered that are similar to the famous and well-described Beta Pictoris system. Like Beta Pictoris, these systems include a young A-type star, a circumstellar gas-poor debris disk, and infalling exocomets. The presence of comets has been inferred from night-to-night changes in the absorption-line characteristics of the circumstellar disk CaII K-line at 3933Å towards these stars. As described by the Falling Evaporated Bodies model of Beust et al (1990, 1998), comet-like planetesimals residing in the outer regions of the dust disk are perturbed into eccentric star-grazing orbits by the action of either mutual collisions or by the gravitational influence of an accompanying massive exoplanet. The plume of gas is liberated at the comet’s close approach to the star.We present new high resolution absorption spectra of the CaII K line recorded over several nights towards the nearby and young (< 50 Myr) A-type stars HD 80007 and HD 109573. Both stars exhibit circumstellar absorption variability that is similar to that frequently observed in other `exocomet-systems’, such as Beta Pictoris and 49 Ceti. We also present a list of the physical characteristics of ~40 A-type stars with associated debris disks that possess circumstellar absorption spectra of the CaII K-line observed by us over several nights. Using all of these data we comment on which stellar parameter(s) seem to be the most important in determining whether or not exocomets will be detected in a given system.

Montgomery, Sharon Lynn; Welsh, Barry; Bukoski, Benjamin; Strausbaugh, Sarah

2015-01-01

405

High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A  

NASA Technical Reports Server (NTRS)

We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.15" (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a spatial resolution of 0.1" (14 AU). It is inclined by 46 degrees plus or minus 2 degrees as the west side is nearest. Although SED modeling and sub-millimeter imagery suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at the limit of our inner working angle (23AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66 %) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh scattering nor Mie scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with the radii of 30 micrometers is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations and have grown in the circumstellar disk of UX Tau A.

Serabyn, G.; Grady, C. A.; Currie, T.

2012-01-01

406

ISO spectroscopy of circumstellar dust in the Herbig Ae systems AB Aur and HD 163296  

E-print Network

Using both the Short- and Long-wavelength Spectrometers on board the Infrared Space Observatory (ISO), we have obtained infrared spectra of the Herbig Ae systems AB Aur and HD 163296. In addition, we obtained ground-based N band images of HD 163296. Our results can be summarized as follows: (1) The main dust components in AB Aur are amorphous silicates, iron oxide and PAHs; (2) The circumstellar dust in HD 163296 consists of amorphous silicates, iron oxide, water ice and a small fraction of crystalline silicates; (3) The infrared fluxes of HD 163296 are dominated by solid state features; (4) The colour temperature of the underlying continuum is much cooler in HD 163296 than in AB Aur, pointing to the existence of a population of very large (mm sized) dust grains in HD 163296; (5) The composition and degree of crystallization of circumstellar dust are poorly correlated with the age of the central star. The processes of crystallization and grain growth are also not necessarily coupled. This means that either the evolution of circumstellar dust in protoplanetary disks happens very rapidly (within a few Myr), or that this evolution is governed by factors other than stellar mass and age.

M. E. van den Ancker; J. Bouwman; P. R. Wesselius; L. B. F. M. Waters; S. M. Dougherty; E. F. van Dishoeck

2000-02-23

407

A search for diffuse bands in fullerene planetary nebulae: evidence of diffuse circumstellar bands  

NASA Astrophysics Data System (ADS)

Large fullerenes and fullerene-based molecules have been proposed as carriers of diffuse interstellar bands (DIBs). The recent detection of the most common fullerenes (C60 and C70) around some planetary nebulae (PNe) now enable us to study the DIBs towards fullerene-rich space environments. We search DIBs in the optical spectra towards three fullerene-containing PNe (Tc 1, M 1-20, and IC 418). Special attention is given to DIBs which are found to be unusually intense towards these fullerene sources. In particular, an unusually strong 4428 Å absorption feature is a common charateristic of fullerene PNe. Similar to Tc 1, the strongest optical bands of neutral C60 are not detected towards IC 418. Our high-quality (S/N > 300) spectra for PN Tc 1, together with its large radial velocity, permit us to search for the presence of diffuse bands of circumstellar origin, which we refer to as diffuse circumstellar bands (DCBs). We report the first tentative detection of two DCBs at 4428 and 5780 Å in the fullerene-rich circumstellar environment around the PN Tc 1. Laboratory and theoretical studies of fullerenes in their multifarious manifestations (carbon onions, fullerene clusters, or even complex species formed by fullerenes and other molecules like PAHs or metals) may help solve the mystery of some of the diffuse band carriers. Appendix A is available in electronic form at http://www.aanda.org

Díaz-Luis, J. J.; García-Hernández, D. A.; Kameswara Rao, N.; Manchado, A.; Cataldo, F.

2015-01-01

408

Atomic Hydrogen in the Extended Circumstellar Envelope of the Carbon Star IRC+10216  

NASA Astrophysics Data System (ADS)

IRC+10216 (CW Leo) is the nearest and best-known carbon star. It is currently undergoing a high rate of mass loss 10-5 M? yr-1) and is believed to be approaching the end of its lifetime on the asymptotic giant branch. Mass loss from IRC+10216 has led to the formation of an extensive circumstellar envelope (CSE) that spans more than half a degree (>1.3 parsecs) across and is both structurally and chemically complex. While the CSE of IRC+10216 has been widely studied through emission from dust and molecular lines, the properties of the predominant CSE constituent—hydrogengas—have remained poorly known, including the total mass and extent of the circumstellar hydrogen and the ratio of atomic to molecular hydrogen throughout the envelope. I will present new insights into these questions based on a study of IRC+10216 in the HI 21-cm lineusing the Very Large Array and the Robert C. Byrd Green Bank Telescope. I will also highlight the value of HI line emission as a probe of the interface between the circumstellar and interstellar environment of the star.

Matthews, Lynn D.

2014-06-01

409

New Frontiers in Circumstellar Science with MagAO's Visible Light Simultaneous Differential Imaging Mode  

NASA Astrophysics Data System (ADS)

We report first light results from the revolutionary Simultaneous Differential Imaging (SDI) mode of the Magellan Adaptive Optics (MagAO) system. This visible light AO imaging mode allows for high contrast differential imaging at resolutions as high as 20mas in hydrogen-alpha, [OI] and [SII]. Simultaneous acquisition of a continuum PSF allows for simple and robust PSF subtraction, opening up even the innermost regions of circumstellar disks to direct imaging. Early results include the first circumstellar disk imaged in silhouette at visible wavelengths with adaptive optics and the tightest (83mas) directly imaged young stellar companion to date, among others. The particular success of the H-alpha SDI imaging mode has led us to embark on the Giant Accreting Planets Survey (GAPlanetS), which will survey 15+ nearby transitional circumstellar disks in search of accreting protoplanets. We will report on plans for this survey and discuss current and future science plans, upgrades and capabilities for MagAO SDI.

Follette, K.; Close, L.; Males, J.; Morzinski, K.; Wu, Y.-L.

2014-03-01

410

Constraints on Circumstellar Dust Grain Sizes from High Spatial Resolution Observations in the Thermal Infrared  

NASA Technical Reports Server (NTRS)

We describe how high spatial resolution imaging of circumstellar dust at a wavelength of about 10 micron, combined with knowledge of the source spectral energy distribution, can yield useful information about the sizes of the individual dust grains responsible for the infrared emission. Much can be learned even when only upper limits to source size are available. In parallel with high-resolution single-telescope imaging that may resolve the more extended mid-infrared sources, we plan to apply these less direct techniques to interpretation of future observations from two-element optical interferometers, where quite general arguments may be made despite only crude imaging capability. Results to date indicate a tendency for circumstellar grain sizes to be rather large compared to the Mathis-Rumpl-Nordsieck size distribution traditionally thought to characterize dust in the general interstellar medium. This may mean that processing of grains after their initial formation and ejection from circumstellar atmospheres adjusts their size distribution to the ISM curve; further mid-infrared observations of grains in various environments would help to confirm this conjecture.

Bloemhof, E. E.; Danen, R. M.; Gwinn, C. R.

1996-01-01

411

Mapping the Nearest Stars for Exotic Habitable Worlds  

NASA Astrophysics Data System (ADS)

Exoplanets are planets orbiting stars other than the sun. Thousands of exoplanets are known and thousands of more planet candidates have been found. Until now, the dominant focus on habitable worlds has been on Earth-like planets, because Earth is the only known planet with life. Yet exoplanets are astonishingly diverse—in terms of their masses, densities, orbits, and host star types—and this diversity motivates a radical extension of what conventionally constitutes a habitable planet. The race to find habitable exoplanets has accelerated with the realization that “big Earths” transiting small stars can be both discovered and characterized with current technology. Moreover, technology for space-based direct imaging of Earth analogs has been rapidly maturing. The ambitious goal of inferring signs of life via biosignature gases in an exoplanet atmosphere, once only a futuristic thought, is now within reach.

Seager, Sara

2014-06-01

412

Spacecraft Habitable Volume: Results of an Interdisciplinary Workshop  

NASA Technical Reports Server (NTRS)

NASA's Human Exploration Framework Team posed the question: "Is 80 cubic meters per person of habitable volume acceptable for a proposed Deep Space Habitat?" The goal of the workshop was to address the "net habitable volume" necessary for long-duration human spaceflight missions and identify design and psychological issues and mitigations. The objectives were: (1) Identify psychological factors -- i.e., "stressors" -- that impact volume and layout specifications for long duration missions (2) Identify mitigation strategies for stressors, especially those that can be written as volume design specifications (3) Identify a forward research roadmap -- i.e., what future work is needed to define and validate objective design metrics? (4) Provide advisories on the human factors consequences of poor net habitable volume allocation and layout design.

Fitts, David J.; Connolly, Janis; Howard, Robert

2011-01-01

413

Plate tectonics and planetary habitability: current status and future challenges.  

PubMed

Plate tectonics is one of the major factors affecting the potential habitability of a terrestrial planet. The physics of plate tectonics is, however, still far from being complete, leading to considerable uncertainty when discussing planetary habitability. Here, I summarize recent developments on the evolution of plate tectonics on Earth, which suggest a radically new view on Earth dynamics: convection in the mantle has been speeding up despite its secular cooling, and the operation of plate tectonics has been facilitated throughout Earth's history by the gradual subduction of water into an initially dry mantle. The role of plate tectonics in planetary habitability through its influence on atmospheric evolution is still difficult to quantify, and, to this end, it will be vital to better understand a coupled core-mantle-atmosphere system in the context of solar system evolution. PMID:22256796

Korenaga, Jun

2012-07-01

414

Habitability of Mars: hyperthermophiles in permafrost  

NASA Astrophysics Data System (ADS)

This is a first microbiological study of volcanic permafrost carried out on Kluchevskaya volcano group (Kamchatka Peninsula) and Deception Island (Antarctica). By culture-and culture-independent methods we showed the presence of viable hyper(thermophilic) microorganisms and their genes within volcanic permafrost. The optimal temperature for sulfide producing bacteria was 65, whereas acetogens and methanogens were able to produce acetate and methane at temperatures up to 75o C, while sulphur-reducers showed optimal growth at 85-92o C. Hy-per(thermophiles) were never found in permafrost outside the volcanic areas before. The only way they are to appear within a frozen material is a concurrent deposition during the eruption, together with products associated with volcano heated subsurface geothermal oases. The elo-quent evidence to the hypothesis is the presence among clones of the