Estimations of orbital parameters of exoplanets from transit photometry by using dynamical constraints     

Zsolt Sándor 《Celestial Mechanics and Dynamical Astronomy》2006,95(1-4):273-285

The probability of the detection of Earth-like exoplanets may increase in the near future after the launch of the space missions using the transit photometry as observation method. By using this technique only the semi-major axis of the detected planet can be determined, and there will be no information on the upper limit of its orbital eccentricity. However, the orbital eccentricity is a very important parameter, not only from a dynamical point of view, since it gives also information on the climate and the habitability of the Earth-like planets. In this paper a possible procedure is suggested for confining the eccentricity of an exoplanet discovered by transit photometry if an already known giant planet orbits also in the system.  相似文献   

Super earth explorer: a coronagraphic off-axis space telescope     

J. Schneider  A. Boccaletti  D. Mawet  P. Baudoz  J.-L. Beuzit  R. Doyon  M. Marley  D. Stam  G. Tinetti  W. Traub  J. Trauger  A. Aylward  J. Y-K. Cho  C.-U. Keller  S. Udry 《Experimental Astronomy》2009,23(1):357-377

The Super-Earth Explorer is an Off-Axis Space Telescope (SEE-COAST) designed for high contrast imaging. Its scientific objective is to make the physico-chemical characterization of exoplanets possibly down to 2 Earth radii. For that purpose it will analyze the spectral and polarimetric properties of the parent starlight reflected by the planets, in the wavelength range 400–1,250 nm.  相似文献   

Could CoRoT-7b and Kepler-10b be remnants of evaporated gas or ice giants?     

Leitzinger M  Odert P  Kulikov YN  Lammer H  Wuchterl G  Penz T  Guarcello MG  Micela G  Khodachenko ML  Weingrill J  Hanslmeier A  Biernat HK  Schneider J 《Planetary and Space Science》2011,59(13):1472-1481

We present thermal mass loss calculations over evolutionary time scales for the investigation if the smallest transiting rocky exoplanets CoRoT-7b (∼1.68R_Earth) and Kepler-10b (∼1.416R_Earth) could be remnants of an initially more massive hydrogen-rich gas giant or a hot Neptune-class exoplanet. We apply a thermal mass loss formula which yields results that are comparable to hydrodynamic loss models. Our approach considers the effect of the Roche lobe, realistic heating efficiencies and a radius scaling law derived from observations of hot Jupiters. We study the influence of the mean planetary density on the thermal mass loss by placing hypothetical exoplanets with the characteristics of Jupiter, Saturn, Neptune, and Uranus to the orbital location of CoRoT-7b at 0.017 AU and Kepler-10b at 0.01684 AU and assuming that these planets orbit a K- or G-type host star. Our findings indicate that hydrogen-rich gas giants within the mass domain of Saturn or Jupiter cannot thermally lose such an amount of mass that CoRoT-7b and Kepler-10b would result in a rocky residue. Moreover, our calculations show that the present time mass of both rocky exoplanets can be neither a result of evaporation of a hydrogen envelope of a “Hot Neptune” nor a “Hot Uranus”-class object. Depending on the initial density and mass, these planets most likely were always rocky planets which could lose a thin hydrogen envelope, but not cores of thermally evaporated initially much more massive and larger objects.  相似文献   

Near 2:1 Mean Motion Resonance Capture and Orbital Evolution of a Hot-Neptune System: HD 106315     

HUANG Xiu-min  JI Jiang-hui  DONG Yao 《Chinese Astronomy and Astrophysics》2021,45(1):99-117

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Emission of cyclotron radiation by interstellar planets     

H. Vanhamäki 《Planetary and Space Science》2011,59(9):862-869

In the solar system all planets that have significant magnetic fields also emit electron cyclotron radiation, usually near the auroral regions around the magnetic poles. In this study we use scaling laws based on solar system data to estimate the power and frequency of the auroral cyclotron emissions from interstellar planets (or sub-brown dwarfs). The emission can be powered either by motion of the planet through the interstellar plasma or by unipolar induction due to a moon. According to our results, in interstellar space the unipolar induction mechanism is potentially more effective than the motional emission mechanism. Typical emission power is around 10¹⁰-10¹² W, but significantly stronger emissions are obtained in the most optimistic estimates. We have to conclude that detection of a rogue Jupiter would be very difficult, if not impossible with the radio telescopes available now or in the near future, but in very favorable conditions a much more massive and rapidly rotating (or otherwise strongly magnetized) gas giant with a large nearby moon could be detected up to ∼57 pc distance with the square kilometer array. There may be a few thousand large enough interstellar planets this close to the solar system. For reference, we point out that according to previous studies some known hot Jupiters are expected to emit up to 10¹⁴-10¹⁶ W of cyclotron radiation, orders of magnitude more than the typical interstellar planets discussed here. However, these emissions have not yet been detected.  相似文献   

Mass loss from “Hot Jupiters”—Implications for CoRoT discoveries, Part II: Long time thermal atmospheric evaporation modeling     

T. Penz  N.V. Erkaev  D. Langmayr  G. Micela  H.K. Biernat  F. Selsis  M. Deleuil 《Planetary and Space Science》2008,56(9):1260-1272

We investigate the efficiency of the atmospheric mass loss due to hydrodynamic blow-off over the lifetime of the exoplanet HD209458b by studying numerically its hydrogen wind for host star X-ray and EUV (XUV) fluxes between 1 and 100 times that of the present Sun. We apply a time-dependent numerical algorithm which is able to solve the system of hydrodynamic equations straight through the transonic point of the flow including Roche lobe effects. The mass loss rates are calculated as functions of the absorbed energy in the thermosphere. Depending on the heating efficiency for a hydrogen-rich thermosphere the maximum temperature obtained in our study at 1.5R_pl by neglecting IR cooling is about 5000-10,000 K for heating efficiencies of 10% and 60%, respectively. We find that the upper atmosphere of HD209458b experiences hydrodynamic blow-off even at such low temperatures if one does not neglect gravitational effects caused by the proximity of the planet to its Roche lobe boundary. Depending on the heating efficiency, we find from the solution of the hydrodynamic equations of mass, momentum, and energy balance that energy-limited mass loss rate estimations overestimate the realistic mass loss rate at present time for HD209458b by several times. Using the maximum heating efficiency for hydrogen-rich atmospheres of 60% we find that HD209458b may experience an atmospheric mass loss rate at present time of about . The mass loss rate evolves to higher values for higher XUV fluxes expected during the early period of the planet's host star evolution, reaching values of several times . The integrated mass loss is found to be between 1.8% and 4.4% of the present mass of HD209458b. We found that the influence of the stellar tidal forces on atmospheric loss (the Roche lobe effect) is not significant at 0.045 AU. For a similar exoplanet, but at closer orbital distances , the combined effect of the Roche lobe and the high XUV radiation result in much higher thermal loss rates of about and even more for early stages. This leads to a total loss over 4 Gyr of 27.5% of the planetary mass.  相似文献   

PLATO: PLAnetary Transits and Oscillations of stars     

Claude Catala 《Experimental Astronomy》2009,23(1):329-356

The PLAnetary Transits and Oscillations of stars Mission (PLATO), presented to ESA in the framework of its “Cosmic Vision” programme, will detect and characterize exoplanets by means of their transit signature in front of a very large sample of bright stars, and measure the seismic oscillations of the parent stars orbited by these planets in order to understand the properties of the exoplanetary systems. PLATO is the next-generation planet finder, building on the accomplishments of CoRoT and Kepler: i) it will observe significantly more stars, ii) its targets will be 2 to 3 magnitudes brighter (hence the precision of the measurements will be correspondingly greater as will be those of post-detection investigations, e.g. spectroscopy, asteroseismology, and eventually imaging), iii) it will be capable of observing significantly smaller exoplanets. The space-based observations will be complemented by ground- and space-based follow-up observations. These goals will be achieved by a long-term (4 years), high-precision, high-time-resolution, high-duty-cycle monitoring in visible photometry of a sample of more than 100,000 relatively bright (m _V  ≤ 12) stars and another 400,000 down to m _V  = 14. Two different mission concepts are proposed for PLATO: i) a “staring” concept with 100 small, very wide-field telescopes, assembled on a single platform and all looking at the same 26° diameter field, and ii) a “spinning” concept with three moderate-size telescopes covering more than 1400 degree². See for The PLATO Consortium.  相似文献   

Starspots     

Klaus G. Strassmeier 《Astronomy and Astrophysics Review》2009,17(3):251-308

Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere (Biermann in Astronomische Nachrichten 264:361, 1938; Z Astrophysik 25:135, 1948). As such, starspots are observable tracers of the yet unknown internal dynamo activity and allow a glimpse into the complex internal stellar magnetic field structure. Starspots also enable the precise measurement of stellar rotation which is among the key ingredients for the expected internal magnetic topology. But whether starspots are just blown-up sunspot analogs, we do not know yet. This article is an attempt to review our current knowledge of starspots. A comparison of a white-light image of the Sun (G2V, 5 Gyr) with a Doppler image of a young solar-like star (EK Draconis; G1.5V, age 100 Myr, rotation 10 × Ω _Sun) and with a mean-field dynamo simulation suggests that starspots can be of significantly different appearance and cannot be explained with a scaling of the solar model, even for a star of same mass and effective temperature. Starspots, their surface location and migration pattern, and their link with the stellar dynamo and its internal energy transport, may have far reaching impact also for our understanding of low-mass stellar evolution and formation. Emphasis is given in this review to their importance as activity tracers in particular in the light of more and more precise exoplanet detections around solar-like, and therefore likely spotted, host stars.  相似文献   

Dipolar magnetic moment of the bodies of the solar system and the Hot Jupiters     

Hector Javier Durand-Manterola 《Planetary and Space Science》2009,57(12):1405-1411

Context

The planets magnetic field has been explained based on the dynamo theory, which presents as many difficulties in mathematical terms as well as in predictions. It proves to be extremely difficult to calculate the dipolar magnetic moment of the extrasolar planets using the dynamo theory.

Objective

The aim is to find an empirical relationship (justifying using first principles) between the planetary magnetic moment, the mass of the planet, its rotation period and the electrical conductivity of its most conductive layer. Then this is applied to Hot Jupiters.

Method

Using all the magnetic planetary bodies of the solar system and tracing a graph of the dipolar magnetic moment versus body mass parameter, the rotation period and electrical conductivity of the internal conductive layer is obtained. An empirical, functional relation was constructed, which was adjusted to a power law curve in order to fit the data. Once this empirical relation has been defined, it is theoretically justified and applied to the calculation of the dipolar magnetic moment of the extra solar planets known as Hot Jupiters.

Results

Almost all data calculated is interpolated, bestowing confidence in terms of their validity. The value for the dipolar magnetic moment, obtained for the exoplanet Osiris (HD209458b), helps understand the way in which the atmosphere of a planet with an intense magnetic field can be eroded by stellar wind. The relationship observed also helps understand why Venus and Mars do not present any magnetic field.  相似文献   

Darwin—an experimental astronomy mission to search for extrasolar planets     

《Experimental Astronomy》2009,23(1):435-461

As a response to ESA call for mission concepts for its Cosmic Vision 2015–2025 plan, we propose a mission called Darwin. Its primary goal is the study of terrestrial extrasolar planets and the search for life on them. In this paper, we describe different characteristics of the instrument.

Charles S. CockellEmail:

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