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TOPIC: Extrasolar Planets
Blobrana


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RE: Extrasolar Planets
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Title: HAT-P-3b: A heavy-element rich planet transiting a K dwarf star
Authors: G. Torres (1), G. A. Bakos (1,2), G. Kovacs (3), D. W. Latham (1), J. M. Fernandez (1), R. W. Noyes (1), G. A. Esquerdo (1), A. Sozzetti (1,4), D. A. Fischer (5), R. P. Butler (6), G. W. Marcy (7), R. P. Stefanik (1), D. D. Sasselov (1), J. Lazar (8), I. Papp (8), P. Sari (8) ((1)Harvard-Smithsonian Centre for Astrophysics; (2) Hubble Fellow; (3) Konkoly Observatory, Hungary; (4) INAF - Osservatorio Astronomico di Torino, Italy; (5) San Francisco State University; (6) Carnegie Institute of Washington; (7) University of California, Berkeley; (8) Hungarian Astronomical Association, Hungary)

We report the discovery of a Jupiter-size planet transiting a relatively bright (V = 11.56) and metal-rich early K dwarf star with a period of about 2.9 days. On the basis of follow-up photometry and spectroscopy we determine the mass and radius of the planet, HAT-P-3b, to be M_p = 0.599 ± 0.026 M_Jup and R_p = 0.890 ± 0.046 R_Jup. The relatively small size of the object for its mass implies the presence of about 75 Earth masses worth of heavy elements (1/3 of the total mass) based on current theories of irradiated extrasolar giant planets, similar to the mass of the core inferred for the transiting planet HD 149026b. The bulk density of HAT-P-3b is found to be rho_p = 1.06 ± 0.17 g/cm³, and the planet orbits the star at a distance of 0.03894 AU. Ephemerides for the transit centres are T_c = 2,454,218.7594 ± 0.0029 + N (2.899703 ± 0.000054) (HJD).

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Blobrana


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Posts: 131433
Date:
ChaHa8
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Title: 16-20 Jupiter mass RV companion orbiting the brown dwarf candidate ChaHa8
Authors: V. Joergens, A. Mueller (Max-Planck Institute for Astronomy Heidelberg)

We report the discovery of a 16-20 Jupiter mass radial velocity companion around the very young (~3 Myr) brown dwarf candidate ChaHa8 (M5.75-M6.5). Based on high-resolution echelle spectra of ChaHa8 taken between 2000 and 2007 with UVES at the VLT, a companion was detected through RV variability with a semi-amplitude of 1.6 km/s. A Kepler fit to the data yields an orbital period of the companion of 1590 days and an eccentricity of e=0.49. A companion minimum mass M2sini between 16 and 20 Jupiter masses is derived when using model-dependent mass estimates for the primary. The mass ratio q= M2/M1 might be as small as 0.2 and, with a probability of 87%, it is less than 0.4. ChaHa8 harbours most certainly the lowest mass companion detected so far in a close (~ 1 AU) orbit around a brown dwarf or very low-mass star. From the uncertainty in the orbit solution, it cannot completely be ruled out that the companion has a mass in the planetary regime. Its discovery is in any case an important step towards RV planet detections around BDs. Further, ChaHa8 is the fourth known spectroscopic brown dwarf or very low-mass binary system with an RV orbit solution and the second known very young one.

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Blobrana


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Posts: 131433
Date:
RE: Extrasolar Planets
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Title: Characterisation of the hot Neptune GJ 436b with Spitzer and ground-based observations
Authors: B.-O. Demory (1,7), M. Gillon (1,2), T. Barman (3), X. Bonfils (4), M. Mayor (1), T. Mazeh (5), F. Pont (1), D. Queloz (1), S. Udry (1), F. Bouchy (8), X. Delfosse (6), T. Forveille (6), F. Mallmann (7), F. Pepe (1), C. Perrier (6) ((1) Observatoire de Geneve, Universite de Geneve, Switzerland; (2) Institut d'Astrophysique et de Geophysique, Universite de Liege, Belgium; (3) Lowell Observatory, Flagstaff, AZ, USA; (4) Observatorio Astronomico de Lisboa, Lisboa, Portugal; (5) School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Israel; (6) Laboratoire d'Astrophysique de Grenoble, Universite J. Fourier, Grenoble, France; (7) Observatoire Francois-Xavier Bagnoud - OFXB, Saint-Luc, Switzerland; (8) Institut d'Astrophysique de Paris, Universite Pierre & Marie Curie, Paris, France)
(Version v2)

We present Spitzer Space Telescope infrared photometry of a secondary eclipse of the hot Neptune GJ 436b. The observations were obtained using the 8-micron band of the InfraRed Array Camera (IRAC). The data spanning the predicted time of secondary eclipse show a clear flux decrement with the expected shape and duration. The observed eclipse depth of slightly less than 0.5 mag allows us to estimate a blackbody brightness temperature of Tb = 709 ±17 K at 8 microns. We compare this infrared flux measurement to a model of the planetary thermal emission, and show that this model reproduces properly the observed flux decrement. The timing of the secondary eclipse confirms the non-zero orbital eccentricity of the planet, while also increasing its precision (e = 0.14 ± 0.01). Using additional new spectroscopic and photometric observations allows us to estimate the rotational period of the star and to assess to an high extent the dynamics of the system and the potential presence of another planet.

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Blobrana


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Posts: 131433
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HD 98800
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Planets may be present in a quadruple star system 150 light years from Earth, according to Spitzer Space Telescope observations.
The system, called HD 98800, consists of two pairs of stars in which the partners in each pair orbit one another closely. The pairs themselves travel around each other on a very elongated path.
A dusty disc was already known to surround one of the pairs of stars. Now, Elise Furlan of the University of California in Los Angeles, US, and colleagues have made more detailed observations of the disc with Spitzer.
The Spitzer observations suggest the disc is actually made of two concentric rings around the stellar pair. One lies about twice as far as the Earth lies from the Sun, while other, which is denser, lies about six times the Earth-Sun distance.

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Blobrana


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Posts: 131433
Date:
RE: Extrasolar Planets
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Amateur Bags GJ 436 b Transit
One of the most exciting aspects of the exoplanet hunt is that it is not confined to huge telescopes and professional astronomers. Timothy Ferris described the remarkable advances in amateur equipment and observing techniques in Seeing In the Dark (Simon & Schuster, 2002), but hell need a whole new chapter to cover whats happening not only with distributed computing (as via the systemic collaboration, for example) and the software and hardware advances that let amateurs observe exoplanet transits from sites around the world.

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Blobrana


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Posts: 131433
Date:
HD 98800B
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Astronomers used Spitzer's infrared vision to study a dusty disk that swirls around a pair of stars in the quadruple-star system HD 98800. Such disks are thought to give rise to planets. Instead of a smooth, continuous disk, the telescope detected gaps that could be caused by a unique gravitational relationship between the system's four stars. Alternatively, the gaps could indicate planets have already begun to form, carving out lanes in the dust.

HD 98800
An artist concept of the HD 98800 system
 Credit NASA/JPL-Caltech/T. Pyle (SSC-Caltech)

"Planets are like cosmic vacuums. They clear up all the dirt that is in their path around the central stars" - Dr. Elise Furlan, of the NASA Astrobiology Institute at the University of California at Los Angeles.

Furlan is the lead author of a paper that has been accepted for publication in The Astrophysical Journal.
HD 988000 is approximately 10 million years old, and is located 150 light-years away in the constellation TW Hydrae.
Before Spitzer set its gaze on HD 98800, astronomers had a rough idea of the system's structure from observations with ground-based telescopes. They knew the system contains four stars, and that the stars are paired off into doublets, or binaries. The stars in the binary pairs orbit around each other, and the two pairs also circle each other like choreographed ballerinas. One of the stellar pairs, called HD 98800B, has a disk of dust around it, while the other pair has none.

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-- Edited by Blobrana at 21:16, 2007-07-24

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Blobrana


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Posts: 131433
Date:
RE: Extrasolar Planets
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It's boom time for planet hunters. Astronomers are bagging new worlds at an average rate of more than two a month.
As of July 20, the latest available date, 246 extrasolar planets had been detected circling other stars in the Milky Way galaxy. Among them are 25 alien "solar systems" consisting of two, three or four bodies orbiting single suns.

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Blobrana


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Posts: 131433
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Title: UV habitable zones around M stars
Authors: Andrea P. Buccino, Guillermo A. Lemarchand, Pablo J. D. Mauas
(Version v3)

During the last decade, there was a paradigm-shift in order to consider terrestrial planets within liquid-water habitable zones (LW-HZ) around M stars, as suitable places for the emergence and evolution of life. Here we analyse the influence of UV boundary conditions to three planetary systems around dM (HIP 74995, HIP 109388 and HIP 113020). We apply our model of UV habitable zone (UV-HZ) (Buccino et al. 2006) to these cases and show that during the quiescent UV output there would not be enough UV radiation within the LW-HZ in order to trigger biogenic processes. We also analyse the cases of two other M flare stars and show that the flares of moderate intensity could provide the necessary energy to trigger those biogenic processes, while the strong flares not necessary rule-out the possibility of life-bearing planets.

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Blobrana


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Posts: 131433
Date:
GJ 436b
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Title: Spitzer Transit and Secondary Eclipse Photometry of GJ 436b
Authors: Drake Deming, Joseph Harrington, Gregory Laughlin, Sara Seager, Sarah B. Navarro, William C. Bowman, Karen Horning

We report the results of infrared (8 micron) transit and secondary eclipse photometry of the hot Neptune exoplanet, GJ436b using Spitzer. The nearly photon-limited precision of these data allow us to measure an improved radius for the planet, and to detect the secondary eclipse. The transit (centred at HJD = 2454280.78149 ±0.00016) shows the flat-bottomed shape typical of infrared transits, and it precisely defines the planet-to-star radius ratio (0.0839 ±0.0005), independent of the stellar properties. However, we obtain the planetary radius, as well as the stellar mass and radius, by fitting to the transit curve simultaneously with an empirical mass-radius relation for M-dwarfs (M=R). We find Rs=Ms=0.47 ±0.02 in solar units, and Rp=27,600 ±1170 km (4.33 ±0.18 Earth radii). This radius significantly exceeds the radius of a naked ocean planet, and requires a gaseous hydrogen-helium envelope. The secondary eclipse occurs at phase 0.587 ±0.005, proving a significant orbital eccentricity (e=0.15 ±0.012). The amplitude of the eclipse (5.7 ±0.8e-4) indicates a brightness temperature for the planet of T=712 ±36K. If this is indicative of the planet's physical temperature, it suggests the occurrence of tidal heating in the planet. An uncharacterised second planet likely provides ongoing gravitational perturbations, to maintain GJ436b's orbit eccentricity over long time scales.

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Blobrana


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Posts: 131433
Date:
RE: Extrasolar Planets
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Title: A New Planet Around an M Dwarf: Revealing a Correlation Between Exoplanets and Stellar Mass
Authors: John A. Johnson, R. Paul Butler, Geoffrey W. Marcy, Debra A. Fischer, Steven S. Vogt, Jason T. Wright, Kathryn M. G. Peek

We report precise Doppler measurements of GJ317 (M3.5V) that reveal the presence of a planet with a minimum mass Msini = 1.2 Mjup in an eccentric, 692.9 day orbit. GJ317 is only the third M dwarf with a Doppler-detected Jovian planet. The residuals to a single-Keplerian fit show evidence of a possible second orbital companion. The inclusion of an additional Jupiter-mass planet (P = 2700 days, Msini = 0.83 Mjup) improves the quality of fit significantly, reducing the rms from 12.5 m/s to 6.32 m/s. A false-alarm test yields a 1.1% probability that the curvature in the residuals of the single-planet fit is due to random fluctuations, lending additional credibility to the two-planet model. However, our data only marginally constrain a two-planet fit and further monitoring is necessary to fully characterize the properties of the second planet. To study the effect of stellar mass on Jovian planet occurrence we combine our samples of M stars, Solar-mass dwarfs and intermediate-mass subgiants. We find a positive correlation between stellar mass and the occurrence rate of Jovian planets within 2.5 AU; the former A-type stars in our sample are nearly 5 times more likely than the M dwarfs to harbour a giant planet. Our analysis shows that the correlation between Jovian planet occurrence and stellar mass remains even after accounting for the effects of stellar metallicity.

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