Spectral, Spatial, and Time properties of the hydrogen nebula around exoplanet HD209458b

All far ultraviolet observations of HD209458 tend to support a scenario in which the inflated hydrogen atmosphere of its planetary companion strongly absorbs the stellar \lya flux during transit. However, it was not clear how the transit absorption depends on the selected wavelength range in the stellar line profile, nor how the atomic hydrogen cloud was distributed spatially around HD209458b. Here we report a sensitivity study of observed time and spectral variations of the stellar flux. In particular, the sensitivity of the absorption depth during transit to the assumed spectral range in the stellar line profile is shown to be very weak, leading to a transit depth in the range $(8.4-8.9)$ for all possible wavelength ranges, and thereby confirming our initially-reported absorption rate. Taking the ratio of the line profile during transit to the unperturbed line profile, we also show that the spectral signature of the absorption by the exoplanetary hydrogen nebula is symmetric and typical of a Lorentzian, optically thick medium. Our results question the adequacy of models that require a huge absorption and/or a strong asymmetry between the blue and red side of the absorption line during transit as no such features could be detected in the HST FUV absorption profile. Finally, we show that standard atmospheric models of HD209458b provide a good fit to the observed absorption profile during transit. Other hybrid models assuming a standard model with a thin layer of superthermal hydrogen on top remain possible.Comment: 10 pages, 7 figures, accepted for publication in Astrophysical Journa

The ERE of the "Red Rectangle" revisited

We present in this paper high signal-to-noise long-slit optical spectra of the Extended Red Emission (ERE) in the "Red Rectangle" (RR) nebula. These spectra, obtained at different positions in the nebula, reveal an extremely complex emission pattern on top of the broad ERE continuum. It is well known that three features converge at large distance from the central object, in wavelength and profile to the diffuse interstellar bands (DIBs) at 5797, 5849.8 and 6614 ang., (e.g. Sarre et al., 1995). In this paper we give a detailed inventory of all spectral subfeatures observed in the 5550--6850 ang. spectral range. Thanks to our high S/N spectra, we propose 5 new features in the RR that can be associated with DIBs. For the 5550--6200 ang. spectral range our slit position was on top of the NE spike of the X shaped nebula. A detailed description of the spatial profile-changes is given of the strongest features revealing that even far out in the nebula at 24 arcsec from the central star, there remains a small shift in wavelength of 1 respectively 2 ang between the ERE subfeatures and the DIB wavelengths of 5797.11 and 5849.78 ang.Comment: 8 pages, 9 figures accepted by Astronomy and Astrophysic

HST/NICMOS Imaging Polarimetry of Proto-Planetary Nebulae II: Macro-morphology of the Dust Shell Structure via Polarized Light

The structure of the dusty circumstellar envelopes (CSEs) of proto-planetary nebulae (PPNs) reveals the mass-loss history of these sources and how such histories may differ for elliptical (SOLE) and bipolar (DUPLEX) PPNs. To study the PPN structures via dust-scattered linearly polarized starlight, we have compiled the imaging-polarimetric data for all 18 evolved stars that have been obtained to date with NICMOS on-board the Hubble Space Telescope (HST). This alternative imaging technique provides a unique way to probe the distribution of dust grains that scatter light around evolved stars. The new perspective gained from the imaging-polarimetric data has revealed several new aspects to the structures of PPNs. Point-symmetry is a prevalent imaging-polarimetric characteristic resulting from the azimuthal density gradient in the CSEs. Among these point-symmetric nebulae, three detailed morphological types can be differentiated by their polarized intensity, I_pol, and polarization strength, P. While the azimuthal density gradient is reversed above and below the equatorial plane in optically thicker bipolar nebulae, there is no gradient reversal in optically thinner elliptical nebulae. The equatorial plane of the system defined by the integrated angle of polarization is not necessarily orthogonal to the axis of the apparent bipolar structure in the total intensity data.Comment: 27 pages, 14 figures, 3 tables; to appear in the Astronomical Journal March 2007 issu

Solar parameters for modeling interplanetary background

The goal of the Fully Online Datacenter of Ultraviolet Emissions (FONDUE) Working Team of the International Space Science Institute in Bern, Switzerland, was to establish a common calibration of various UV and EUV heliospheric observations, both spectroscopic and photometric. Realization of this goal required an up-to-date model of spatial distribution of neutral interstellar hydrogen in the heliosphere, and to that end, a credible model of the radiation pressure and ionization processes was needed. This chapter describes the solar factors shaping the distribution of neutral interstellar H in the heliosphere. Presented are the solar Lyman-alpha flux and the solar Lyman-alpha resonant radiation pressure force acting on neutral H atoms in the heliosphere, solar EUV radiation and the photoionization of heliospheric hydrogen, and their evolution in time and the still hypothetical variation with heliolatitude. Further, solar wind and its evolution with solar activity is presented in the context of the charge exchange ionization of heliospheric hydrogen, and in the context of dynamic pressure variations. Also the electron ionization and its variation with time, heliolatitude, and solar distance is presented. After a review of all of those topics, we present an interim model of solar wind and the other solar factors based on up-to-date in situ and remote sensing observations of solar wind. Results of this effort will further be utilised to improve on the model of solar wind evolution, which will be an invaluable asset in all heliospheric measurements, including, among others, the observations of Energetic Neutral Atoms by the Interstellar Boundary Explorer (IBEX).Comment: Chapter 2 in the planned "Cross-Calibration of Past and Present Far UV Spectra of Solar System Objects and the Heliosphere", ISSI Scientific Report No 12, ed. R.M. Bonnet, E. Quemerais, M. Snow, Springe