118409122
BETA PICTORIS : Evidence of light variations
We have analyzed Beta Pictoris photometric measurements obtained from La Silla by the Geneva Observatory from 1975 to 1992. These data show evidence of variations in the brightness of the star, with no color dependency. Here, we demonstrate that the light variations are present on long as well as on short time scales. On a long time scale, we show that the apparent magnitude of Beta Pic decreased by 0.011 +/- 0.004 mag from 1979 to 1982. Moreover, when we consider all the measurements, the chance that there is no variation at all can be estimated to be less than 10E-4. On short time scales there is a peculiar feature observed during about 30 days; the variations may be as high as 0.04 magnitude. A maximum entropy reconstruction of the photometric data is tentatively proposed and some physical interpretations are presented.
15772530
Velocity Dispersion of the High Rotational Levels of H2
We present a study of the high rotational bands (J ≥ 2) of H2 toward four early-type Galactic stars: HD 73882, HD 192639, HD 206267, and HD 207538. In each case, the velocity dispersion, characterized by the spectrum fitting parameter b, increases with the level of excitation, a phenomenon that has previously been detected by the Copernicus and IMAPS observatories. In particular, we show with 4 σ confidence that for HD 192639 it is not possible to fit all J levels with a single b-value and that higher b-values are needed for the higher levels. The amplitude of the line broadening, which can be as high as 10 km s-1, makes explanations such as inhomogeneous spatial distribution unlikely. We investigate a mechanism in which the broadening is due to the molecules that are rotationally excited through the excess energy acquired after their formation on a grain (H2 formation pumping). We show that different dispersions would be a natural consequence of this mechanism. We note, however, that such a process would require a formation rate 10 times higher than what was inferred from other observations. In view of this result, and of the difficulty in accounting for the velocity dispersion as thermal broadening (T would be around 10,000 K), we conclude then that we are most certainly observing some highly turbulent warm layer associated with the cold diffuse cloud. Embedded in a magnetic field, it could be responsible for the high quantities of CH+ measured in the cold neutral medium.
7769599
FUSE Observations of Interstellar Gas Towards the LMC Star Sk -67 05
We report on measurements of interstellar O VI, H2, P II, Si II, Ar I, and Fe II absorption along the line of sight to Sk -67 05, a B0 Ia star in a diffuse H II region in the western edge of the Large Magellanic Cloud (LMC). We find log N(O VI) = 14.40 +/- 0.04 in the Milky Way (MW) component and, using the C IV column density from previous IUE observations, N(C IV) / N(O VI) = 1.00 +/- 0.16, a value similar to other halo measurements made with FUSE. In the LMC component, log N(O VI) = 13.89 +/- 0.05, and N(C IV) / N(O VI)<0.4 (3 sigma), since only an upper limit on N(C IV) is available. Along this sightline the LMC is rich in molecular hydrogen, log N(H2) = 19.50 +/- 0.08; in the MW log N(H2) = 14.95 +/- 0.08. A two-component fit for the excitation temperature of the molecular gas in the LMC gives T_01 = 59 +/- 5 K for J=0,1 and T_ex = 800 +/- 330 K for J=3,4,5. For the MW, T_01 = 99 (+30/-20) K; no excitation temperature could be determined for the higher rotational states. The MW and LMC gas-phase [Fe/P] abundances are ~0.6 and ~0.7 dex lower, respectively, than solar system abundances. These values are similar to [Fe/Zn] measurements for the MW and LMC towards SN 1987A.
118472008
Transmission spectrum of Venus as a transiting exoplanet
On 5-6 June 2012, Venus will be transiting the Sun for the last time before 2117. This event is an unique opportunity to assess the feasibility of the atmospheric characterisation of Earth-size exoplanets near the habitable zone with the transmission spectroscopy technique and provide an invaluable proxy for the atmosphere of such a planet. In this letter, we provide a theoretical transmission spectrum of the atmosphere of Venus that could be tested with spectroscopic observations during the 2012 transit. This is done using radiative transfer across Venus' atmosphere, with inputs from in-situ missions such as Venus Express and theoretical models. The transmission spectrum covers a range of 0.1-5 {\mu}m and probes the limb between 70 and 150 km in altitude. It is dominated in UV by carbon dioxide absorption producing a broad transit signal of ~20 ppm as seen from Earth, and from 0.2 to 2.7 {\mu}m by Mie extinction (~5 ppm at 0.8 {\mu}m) caused by droplets of sulfuric acid composing an upper haze layer above the main deck of clouds. These features are not expected for a terrestrial exoplanet and could help discriminating an Earth-like habitable world from a cytherean planet.
14751075
Atmospheric escape from hot Jupiters
The extra-solar planet HD209458b has been found to have an extended atmosphere of escaping atomic hydrogen (Vidal-Madjar et al. 2003), suggesting that "hot Jupiters" closer to their parent stars could evaporate. Here we estimate the atmospheric escape (so called evaporation rate) from hot Jupiters and their corresponding life time against evaporation. The calculated evaporation rate of HD209458b is in excellent agreement with the H i Lyman-� observations. We find that the tidal forces and high temperatures in the upper atmosphere must be taken into account to obtain reliable estimate of the atmospheric escape. Because of the tidal forces, we show that there is a new escape mechanism at intermediate temperatures at which the exobase reaches the Roche lobe. From an energy balance, we can estimate plausible values for the planetary exospheric temperatures, and thus obtain typical life times of planets as a function of their mass and orbital distance.
16667758
FUSE Observations of the HD Molecule toward HD 73882
The Lyman and Werner band systems of deuterated molecular hydrogen (HD) occur in the far UV range below 1200 A. The high sensitivity of the FUSE mission can give access, at moderate resolution, to hot stars shining through translucent clouds, in the hope of observing molecular cores in which deuterium is essentially in the form of HD. Thus, the measurement of the HD/H2 ratio may become a new powerful tool to evaluate the deuterium abundance, D/H, in the interstellar medium. We report here on the detection of HD toward the high extinction star HD 73882 [E(B-V)=0.72]. A preliminary analysis is presented.
200103319
The D0 online monitoring and automatic DAQ recovery
The DZERO experiment, located at the Fermi National Accelerator Laboratory, has recently started the Run 2 physics program. The detector upgrade included a new Data Acquisition/Level 3 Trigger system. Part of the design for the DAQ/Trigger system was a new monitoring infrastructure. The monitoring was designed to satisfy real-time requirements with 1-second resolution as well as nonreal-time data. It was also designed to handle a large number of displays without putting undue load on the sources of monitoring information. The resulting protocol is based on XML, is easily extensible, and has spawned a large number of displays, clients, and other applications. It is also one of the few sources of detector performance available outside the Online System's security wall. A tool, based on this system, which provides for auto-recovery of DAQ errors, has been designed. This talk will include a description of the DZERO DAQ/Online monitor server, based on the ACE framework, the protocol, the auto-recovery tool, and several of the unique displays which include an ORACLE-based archiver and numerous GUIs.
121210028
Field measurements in the Fermilab electron cooling solenoid prototype
To increase the Tevatron luminosity, Fermilab is developing a high-energy electron cooling system [1] to cool 8.9-GeV/c antiprotons in the Recycler ring. The schematic layout of the Recycler Electron Cooling (REC) system is shown in Figure 1. Cooling of antiprotons requires a round electron beam with a small angular spread propagating through a cooling section with a kinetic energy of 4.3 MeV. To confine the electron beam tightly and to keep its transverse angles below 10{sup -4} rad, the cooling section will be immersed into a solenoidal field of 50-150G. As part of the RD also, this chapter shows the results of our first attempts of implementing the algorithm.