astro-ph coffee suggested papers for Thu, Mar 03, 2011 at 03:00:00 PM

astro-ph coffee will be held at the date and time above in the PAB 3rd-floor reading room. Some suggested papers of interest are listed below.

28 Feb 2011

We show that dissipationless LCDM simulations predict that the majority of the most massive subhalos of the Milky Way are too dense to host any of its bright satellites (L_V > 10^5 L_sun). These dark subhalos have circular velocities at infall of 30-70 km/s and infall masses of [0.2-4] x 10^10 M_sun. Unless the Milky Way is a statistical anomaly, this implies that galaxy formation becomes effectively stochastic at these masses. This is in marked contrast to the well-established monotonic rel...

25 Feb 2011

It has recently been reported that the faintest galaxies at z~6-7 display extremely blue UV continuum slopes, with a UV power-law index beta ~ -3. Such slopes are bluer than previously reported for any other galaxy population, and imply extinction-free, young, very low-metallicity stellar populations with a high ionizing photon escape fraction. Here we undertake a critical study of the evidence for such extreme values of beta, combining three new WFC3/IR-selected samples of galaxies spanning ~2...

2 Mar 2011

We report the results of the observation of the nearby satellite galaxy Segue 1 performed by the MAGIC-I ground-based gamma-ray telescope between November 2008 and March 2009 for a total of 43.2 hours. No significant gamma-ray emission was found above the background. Differential upper limits on the gamma-ray flux are derived assuming various power-law slopes for the possible emission spectrum. Integral upper limits are also calculated for several power-law spectra and for different energy thre...

28 Feb 2011

Lyman-alpha (Lya) emission of neutral hydrogen (1215.67 Angstr\"om) is the main contributor to the ultraviolet flux of low-mass stars such as M dwarfs. It is also the main light source used in studies of the evaporating upper atmospheres of transiting extrasolar planets with ultraviolet transmission spectroscopy. However, there are very few observations of the Lya emissions of quiet M dwarfs, and none exist for those hosting exoplanets. Here, we present Lya observations of the hot-neptune host ...

28 Feb 2011

Exoplanets at small orbital distances from their host stars are submitted to intense levels of energetic radiations, X-rays and extreme ultraviolet (EUV). Depending on the masses and densities of the planets and on the atmospheric heating efficiencies, the stellar energetic inputs can lead to atmospheric mass loss. These evaporation processes are observable in the ultraviolet during planetary transits. The aim of the present work is to quantify the mass-loss rates (dm/dt), heating efficiencies ...

28 Feb 2011

We present Hubble Space Telescope optical and near-ultraviolet transmission spectra of the transiting hot-Jupiter HD189733b, taken with the repaired Space Telescope Imaging Spectrograph (STIS) instrument. The resulting spectra cover the range 2900-5700 Ang and reach per-exposure signal-to-noise levels greater than 11,000 within a 500 Ang bandwidth. We used time series spectra obtained during two transit events to determine the wavelength dependance of the planetary radius and measure the exopla...

28 Feb 2011

Context: Only recently it has become possible to measure the thermal emission from hot-Jupiters at near-Infrared wavelengths using ground-based telescopes, by secondary eclipse observations. This allows the planet flux to be probed around the peak of its spectral energy distribution, which is vital for the understanding of its energy budget. Aims: The aim of the reported work is to measure the eclipse depth of the planet HAT-P-1b at 2.2micron. This planet is an interesting case, since the amoun...

28 Feb 2011

Precise infrared radial velocimetry enables the detection and transit verification of low mass extrasolar planets orbiting mid-to-late M dwarf hosts, which are too faint for V-band radial velocity surveys. The TripleSpec Exoplanet Discovery Instrument, or TEDI, is the combination of a variable-delay Michelson interferometer and a medium-resolution (R=2700) near-infrared spectrograph on the Palomar 200" Hale Telescope. We used TEDI to monitor GJ 699, a nearby mid-M dwarf, over 11 nights spread a...

28 Feb 2011

(Abridged) We have identified CFBDSIR J1458+10 as a 0.11" binary using Keck laser guide star AO imaging. We measure a parallactic distance of 23.1+/-2.4 pc to the system based on CFHT near-IR astrometry. We assign a spectral type of T9.5 to the integrated-light near-IR spectrum, and model atmospheres suggest a slightly higher temperature and surface gravity than the T10 dwarf UGPS J0722-05. Thus, CFBDSIR J1458+10AB is the coolest brown dwarf binary to date. Its secondary component has an absolu...

28 Feb 2011

We use a dense redshift survey in the foreground of the Subaru GTO2deg$^2$ weak lensing filed (centered at $\alpha_{2000}$ = 16$^h04^m44^s$;$\delta_{2000}$ =43$^\circ11^{\prime}24^{\prime\prime}$) to assess the completeness and efficiency of massive halo identification in the weak lensing map. The redshift survey (published here) includes 4541 galaxies; 4405 are new redshifts measured with the Hectospec on the MMT. Among the weak lensing peaks with a signal-to-noise greater that 3.7, only 50% c...

25 Feb 2011

We report the discovery of the 20.7-ms binary pulsar J1952+2630, made using the distributed computing project Einstein@Home in Pulsar ALFA survey observations with the Arecibo telescope. Follow-up observations with the Arecibo telescope confirm the binary nature of the system. We obtain a circular orbital solution with an orbital period of 9.4 hr, a projected orbital radius of 2.8 lt-s, and a mass function of f = 0.15 solar masses by analysis of spin period measurements. No evidence of orbital ...

25 Feb 2011

Astrometric Very Long Baseline Interferometry (VLBI) observations of maser sources in the Milky Way are used to map the spiral structure of our Galaxy and to determine fundamental parameters such as the rotation velocity ($\Theta_0$) and curve and the distance to the Galactic center (R$_0$). Here, we present an update on our first results, implementing a recent change in the knowledge about the Solar motion. It seems unavoidable that the IAU recommended values for R$_0$ and $\Theta_0$ need a su...

26 Feb 2011

We have used multi-epoch images from the Infrared Array Camera on board the Spitzer Space Telescope to search for substellar companions to stars in the solar neighborhood based on common proper motions. Through this work, we have discovered a faint companion to the white dwarf WD 0806-661. The comoving source has a projected separation of 130", corresponding to 2500 AU at the distance of the primary (19.2 pc). If it is physically associated, then its absolute magnitude at 4.5um is ~1 mag fainte...

24 Feb 2011

We have generated an extensive new suite of massive giant planet atmosphere models and used it to obtain fits to photometric data for the planets HR 8799b, c, and d. We consider a wide range of cloudy and cloud-free models. The cloudy models incorporate different geometrical and optical thicknesses, modal particle sizes, and metallicities. For each planet and set of cloud parameters, we explore grids in gravity and effective temperature, with which we determine constraints on the planet's mass ...

25 Feb 2011

We present a high-speed, visible-wavelength imaging instrument: MORIS (the MIT Optical Rapid Imaging System). MORIS is mounted on the 3-m Infrared Telescope Facility (IRTF) on Mauna Kea, HI. Its primary component is an Andor iXon camera, a nearly 60 arcsec square field of view with high quantum efficiency, low read noise, low dark current, and full-frame readout rates ranging from as slow as desired to a maximum of between 3.5 Hz and 35 Hz (depending on the mode; read noise of 6e-/pixel and 49 ...

25 Feb 2011

HR8799 is so far the only directly imaged multiple exoplanet system. The orbital configuration would, if better known, provide valuable insight into the formation and dynamical evolution of wide-orbit planetary systems. We present L'-band observations of the HR8799 system obtained with NACO at VLT, adding to the astrometric monitoring of the planets HR8799b, c and d. We investigate how well the two simple cases of (i) a circular orbit and (ii) a face-on orbit fit the astrometric data for HR8799...

astroph.py v0.91ijc based on the original astroph.py. Updated 2011/03/03 11:53:51

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