Dust observations of Comet 9P/Tempel 1 at the time of the Deep Impact

On 4 July 2005 at 05:52 UT, the impactor of NASA's Deep Impact (DI) mission crashed into comet 9P/Tempel 1 with a velocity of about 10 km/s. The material ejected by the impact expanded into the normal coma, produced by ordinary cometary activity. The characteristics of the non-impact coma and cloud produced by the impact were studied by observations in the visible wavelengths and in the near-IR. The scattering characteristics of the "normal" coma of solid particles were studied by comparing images in various spectral regions, from the UV to the near-IR. For the non-impact coma, a proxy of the dust production has been measured in various spectral regions. The presence of sublimating grains has been detected. Their lifetime was found to be about 11 hours. Regarding the cloud produced by the impact, the total geometric cross section multiplied by the albedo was measured as a function of the color and time. The projected velocity appeared to obey a Gaussian distribution with the average velocity of the order of 115 m/s. By comparing the observations taken about 3 hours after the impact, we have found a strong decrease in the cross section in J filter, while that in Ks remained almost constant. This is interpreted as the result of sublimation of grains dominated by particles of sizes of the order of some microns.Comment: Accepted by A&

Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations

Context: Pluto possesses a thin atmosphere, primarily composed of nitrogen, in which the detection of methane has been reported. Aims: The goal is to constrain essential but so far unknown parameters of Pluto's atmosphere such as the surface pressure, lower atmosphere thermal stucture, and methane mixing ratio. Methods: We use high-resolution spectroscopic observations of gaseous methane, and a novel analysis of occultation light-curves. Results: We show that (i) Pluto's surface pressure is currently in the 6.5-24 microbar range (ii) the methane mixing ratio is 0.5+/-0.1 %, adequate to explain Pluto's inverted thermal structure and ~100 K upper atmosphere temperature (iii) a troposphere is not required by our data, but if present, it has a depth of at most 17 km, i.e. less than one pressure scale height; in this case methane is supersaturated in most of it. The atmospheric and bulk surface abundance of methane are strikingly similar, a possible consequence of the presence of a CH4-rich top surface layer.Comment: AA vers. 6.1, LaTeX class for Astronomy & Astrophysics, 9 pages with 5 figures Astronomy and Astrophysics Letters, in pres

Variability of Brown Dwarfs

Brown dwarfs constitute a missing link between low-mass stars and giant planets. Their atmospheres display chemical species typical of planets, and one could wonder whether they also have weather-like patterns. While brown dwarf surface features cannot be directly resolved, the photometric and spectroscopic modulations induced by these features, as they rotate in and out of view, provide a wealth of information on the evolution of their atmosphere. A review of brown dwarfs variability through the L, T and Y spectral types sequence is presented, as well as the constraints that they set on the nature of weather-like patterns on their surface.Comment: Accepted chapter in the "Handbook of Exoplanets"; Springe

The break-up of periodic comet Schwassmann-Wachmann 3: image documents from La Silla telescopes.

The splitting of SW3 in 1995 was an other example of how brittle cometary nuclei are. Unlike in most previous events, however, the break-up of SW3 is well documented by high-quality ground-based observations. SW3 represents an excellent candidate for a comprehensive analysis of cometary fragmentation, which could lead to a better understanding of the the disintegration processes involved in the evolution of comets

Observations of Comet 73P/SW3 close to its closest approach to the Earth.

In May 2006 comet 73P/SW3 passed at less than 0.1 AU from Earth providing us an unique opportunity for high spatial resolution study of its coma. This event was expected to be particularly interesting because the comet had broken apart in 3-4 fragments in 1996. The 2006 apparition has been even more interesting because the fragments produced in 1996, when approaching the Sun, were continuously breaking apart. This process resulted in many small sub-fragments and in the injection in the coma of fresh material, coming from the interior of the nuclei, giving the possibility to study this uncontaminated material. The breaking fragments have been observed at ESO in the visible and near-IR with the aim of analyzing this fresh solid component of the coma in search of possible presence of organic solids. In the presentation we will report preliminary results of this campaign

Novel infrared polarimeter for the ESO CRIRES plus instrument

The CRIRES infrared spectrograph at the European Southern Observatory (ESO) Very Large Telescope (VLT) facility will soon receive an upgrade. This upgrade will include the addition of a module for performing highresolution spectropolarimetry. The polarimetry module will incorporate a novel infrared beamsplitter based on polarization gratings (PGs). The beamsplitter produces a pair of infrared output beams, with opposite circular polarizations, which are then fed into the spectrograph. Visible light passes through the module virtually unaltered and is then available for use by the CRIRES adaptive optics system. We present the design of the polarimetry module and measurements of PG behavior in the 1 to 2.7 μm wavelength range

Wavelength calibration from 1-5 mu m for the CRIRES plus high-resolution spectrograph at the VLT

CRIRES at the VLT is one of the few adaptive optics enabled instruments that offer a resolving power of 105 from 1 - 5 μm. An instrument upgrade (CRIRES+) is proposed to implement cross-dispersion capabilities, spectro-polarimetry modes, a new detector mosaic, and a new gas absorption cell. CRIRES+ will boost the simultaneous wavelength coverage of the current instrument (~ γ/70 in a single-order) by a factor of 10 in the cross-dispersed configuration, while still retaining a ~> 10 arcsec slit suitable for long-slit spectroscopy. CRIRES+ dramatically enhances the instrument's observing efficiency, and opens new scientific opportunities. These include high-precision radial-velocity studies on the 3 m/s level to characterize extra-solar planets and their athmospheres, which demand for specialized, highly accurate wavelength calibration techniques. In this paper, we present a newly developed absorption gas-cell to enable high-precision wavelength calibration for CRIRES+. We also discuss the strategies and developments to cover the full operational spectral range (1 - 5 μµm), employing cathode emission lamps, Fabry-Perot etalons, and absorption gas-cells