Observatoire De Haute-Provence Research Articles

Isoprene emission potentials from European oak forests derived from canopy flux measurements: an assessment of uncertainties and inter-algorithm variability

Abstract. Biogenic emission algorithms predict that oak forests account for ∼ 70 % of the total European isoprene budget. Yet the isoprene emission potentials (IEPs) that underpin these model estimates are calculated from a very limited number of leaf-level observations and hence are highly uncertain. Increasingly, micrometeorological techniques such as eddy covariance are used to measure whole-canopy fluxes directly, from which isoprene emission potentials can be calculated. Here, we review five observational datasets of isoprene fluxes from a range of oak forests in the UK, Italy and France. We outline procedures to correct the measured net fluxes for losses from deposition and chemical flux divergence, which were found to be on the order of 5–8 and 4–5 %, respectively. The corrected observational data were used to derive isoprene emission potentials at each site in a two-step process. Firstly, six commonly used emission algorithms were inverted to back out time series of isoprene emission potential, and then an average isoprene emission potential was calculated for each site with an associated uncertainty. We used these data to assess how the derived emission potentials change depending upon the specific emission algorithm used and, importantly, on the particular approach adopted to derive an average site-specific emission potential. Our results show that isoprene emission potentials can vary by up to a factor of 4 depending on the specific algorithm used and whether or not it is used in a big-leaf or canopy environment (CE) model format. When using the same algorithm, the calculated average isoprene emission potential was found to vary by as much as 34 % depending on how the average was derived. Using a consistent approach with version 2.1 of the Model for Emissions of Gases and Aerosols from Nature (MEGAN), we derive new ecosystem-scale isoprene emission potentials for the five measurement sites: Alice Holt, UK (10 500 ± 2500 µg m−2 h−1); Bosco Fontana, Italy (1610 ± 420 µg m−2 h−1); Castelporziano, Italy (121 ± 15 µg m−2 h−1); Ispra, Italy (7590 ± 1070 µg m−2 h−1); and the Observatoire de Haute Provence, France (7990 ± 1010 µg m−2 h−1). Ecosystem-scale isoprene emission potentials were then extrapolated to the leaf-level and compared to previous leaf-level measurements for Quercus robur and Quercus pubescens, two species thought to account for 50 % of the total European isoprene budget. The literature values agreed closely with emission potentials calculated using the G93 algorithm, which were 85 ± 75 and 78 ± 25 µg g−1 h−1 for Q. robur and Q. pubescens, respectively. By contrast, emission potentials calculated using the G06 algorithm, the same algorithm used in a previous study to derive the European budget, were significantly lower, which we attribute to the influence of past light and temperature conditions. Adopting these new G06 specific emission potentials for Q. robur (55 ± 24 µg g−1 h−1) and Q. pubescens (47 ± 16 µg g−1 h−1) reduced the projected European budget by ∼ 17 %. Our findings demonstrate that calculated isoprene emission potentials vary considerably depending upon the specific approach used in their calculation. Therefore, it is our recommendation that the community now adopt a standardised approach to the way in which micrometeorological flux measurements are corrected and used to derive isoprene, and other biogenic volatile organic compounds, emission potentials.

Masses of the components of SB2 binaries observed with Gaia – IV. Accurate SB2 orbits for 14 binaries and masses of three binaries*

The orbital motion of non-contact double-lined spectroscopic binaries (SB2), with periods of a few tens of days to several years, holds unique accurate informations on individual stellar masses, that only long-term monitoring can unlock. The combination of radial velocity measurements from high-resolution spectrographs and astrometric measurements from high-precision interferometers allows the derivation of SB2 components masses down to the percent precision. Since 2010, we observed a large sample of SB2 with the SOPHIE spectrograph at the Observatoire de Haute-Provence, aiming at the derivation of orbital elements with sufficient accuracy to obtain masses of components with relative errors as low as 1$\%$ when the astrometric measurements of the Gaia satellite will be taken into account. In this paper we present the results from six years of observations of 14 SB2 systems with periods ranging from 33 to 4185 days. Using the TODMOR algorithm we computed radial velocities from the spectra, and then derived the orbital elements of these binary systems. The minimum masses of the 28 stellar components are then obtained with a sample average accuracy of 1.0$\pm$0.2$\,\%$. Combining the radial velocities with existing interferometric measurements, we derived the masses of the primary and secondary components of HIP 61100, HIP 95995 and HIP 101382 with relative errors for components (A,B) of respectively (2.0, 1.7)$\,\%$, (3.7, 3.7)$\,\%$, and (0.2, 0.1)$\,\%$. Using the Cesam2k stellar evolution code, we could constrain the initial He-abundance, age and metallicity for HIP 61100 and HIP 95995.

MOLYBDENUM AND RUTHENIUM ABUNDANCES IN COOL STARS OF THE GALACTIC DISC

We revise the molybdenum and ruthenium abundances in FGK stars with metallicities ranging from −1.0 < [Fe/H] < +0.3. The observed stars belong to the substructures of the Galaxy. The observations were conducted using the 1.93 m telescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle type spectrographs ELODIE and SOPHIE. The results are based on analyses of spectra that have a typical S/N ~ 100-300 and a resolution of 42 000. These estimates were obtained using synthetic spectra computed with LTE model atmosphere.

First observation of Hα redshifted emission in RR Lyr

Context. The so-called Hα third emission occurs around pulsation phase ϕ = 0.30. It has been observed for the first time in 2011 in some RR Lyrae stars. The emission intensity is very weak, and its profile is a tiny persistent hump in the red side-line profile. Aims. We report the first observation of the Hα third emission in RR Lyr itself (HD 182989), the brightest RR Lyrae star in the sky. Methods. New spectra were collected in 2013−2014 with the AURELIE spectrograph (resolving power R = 22 700, T152, Observatoire de Haute-Provence, France) and in 2016−2017 with the eShel spectrograph (R = 11 000, T035, Observatoire de Chelles, France). In addition, observations obtained in 1997 with the ELODIE spectrograph (R = 42 000, T193, Observatoire de Haute-Provence, France) were reanalyzed. Results. The Hα third emission is clearly detected in the pulsation phase interval ϕ = 0.188−0.407, that is, during about 20% of the period. Its maximum flux with respect to the continuum is about 13%. The presence of this third emission and its strength both seem to depend only marginally on the Blazhko phase. The physical origin of the emission is probably due to the infalling motion of the highest atmospheric layers, which compresses and heats the gas that is located immediately above the rising shock wave. The infalling velocity of the hot compressed region is supersonic, almost 50 km s-1, while the shock velocity may be much lower in these pulsation phases. Conclusions. When the Hα third emission appears, the shock is certainly no longer radiative because its intensity is not sufficient to produce a blueshifted emission component within the Hα profile. At phase ϕ = 0.40, the shock wave is certainly close to its complete dissipation in the atmosphere.

Variability and evolution of the midlatitude stratospheric aerosol budget from 22 years of ground-based lidar and satellite observations

Abstract. The article presents new high-quality continuous stratospheric aerosol observations spanning 1994–2015 at the French Observatoire de Haute-Provence (OHP, 44° N, 6° E) obtained by two independent, regularly maintained lidar systems operating within the Network for Detection of Atmospheric Composition Change (NDACC). Lidar series are compared with global-coverage observations by Stratospheric Aerosol and Gas Experiment (SAGE II), Global Ozone Monitoring by Occultation of Stars (GOMOS), Optical Spectrograph and InfraRed Imaging System (OSIRIS), Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and Ozone Mapping Profiling Suite (OMPS) satellite instruments, altogether covering the time span of OHP lidar measurements. Local OHP and zonal-mean satellite series of stratospheric aerosol optical depth are in excellent agreement, allowing for accurate characterization of stratospheric aerosol evolution and variability at northern midlatitudes during the last 2 decades. The combination of local and global observations is used for a careful separation between volcanically perturbed and quiescent periods. While the volcanic signatures dominate the stratospheric aerosol record, the background aerosol abundance is found to be modulated remotely by the poleward transport of convectively cleansed air from the deep tropics and aerosol-laden air from the Asian monsoon region. The annual cycle of background aerosol at midlatitudes, featuring a minimum during late spring and a maximum during late summer, correlates with that of water vapor from the Aura Microwave Limb Sounder (MLS). Observations covering two volcanically quiescent periods over the last 2 decades provide an indication of a growth in the nonvolcanic component of stratospheric aerosol. A statistically significant factor of 2 increase in nonvolcanic aerosol since 1998, seasonally restricted to late summer and fall, is associated with the influence of the Asian monsoon and growing pollution therein.

Discovery of XO-6b: A Hot Jupiter Transiting a Fast Rotating F5 Star on an Oblique Orbit

Abstract Only a few hot Jupiters are known to orbit around fast rotating stars. These exoplanets are harder to detect and characterize and may be less common than around slow rotators. Here, we report the discovery of the transiting hot Jupiter XO-6b, which orbits a bright, hot, and fast rotating star: V = 10.25, T eff⋆ = 6720 ± 100 K, v sin i ⋆ = 48 ± 3 km s−1. We detected the planet from its transits using the XO instruments and conducted a follow-up campaign. Because of the fast stellar rotation, radial velocities taken along the orbit do not yield the planet’s mass with a high confidence level, but we secure a 3σ upper limit M p < 4.4 M Jup. We also obtain high-resolution spectroscopic observations of the transit with the SOPHIE spectrograph at the 193-cm telescope of the Observatoire de Haute-Provence and analyze the stellar lines profile by Doppler tomography. The transit is clearly detected in the spectra. The radii measured independently from the tomographic analysis and from the photometric light curves are consistent, showing that the object detected by both methods is the same and indeed transits in front of XO-6. We find that XO-6b lies on a prograde and misaligned orbit with a sky-projected obliquity . The rotation period of the star is shorter than the orbital period of the planet: P rot < 2.12 days, P orb = 3.77 days. Thus, this system stands in a largely unexplored regime of dynamical interactions between close-in giant planets and their host stars.

The young open cluster NGC 7067 using Strömgren photometry

Abstract NGC 7067 is a young open cluster located in the direction between the first and the second Galactic quadrants and close to the Perseus spiral arm. This makes it useful for studies of the nature of the Milky Way spiral arms. Strömgren photometry taken with the Wide Field Camera at the Isaac Newton Telescope allowed us to compute individual physical parameters for the observed stars and hence to derive the cluster's physical parameters. Spectra from the 1.93-m telescope at the Observatoire de Haute-Provence helped to check and improve the results. We obtained photometry for 1233 stars, individual physical parameters for 515 and spectra for 9 of them. The 139 selected cluster members lead to a cluster distance of 4.4 ± 0.4 kpc, with an age below log10(t(yr)) = 7.3 and a present mass of 1260 ± 160 M⊙. The morphology of the data reveals that the centre of the cluster is at (α, δ) = (21: 24: 13.69, +48: 00: 39.2) J2000, with a radius of 6.1 arcmin. Strömgren and spectroscopic data allowed us to improve the previous parameters available for the cluster in the literature.

Validation of satellite-based noontime UVI with NDACC ground-based instruments: influence of topography, environment and satellite overpass time

Abstract. Spectral solar UV radiation measurements are performed in France using three spectroradiometers located at very different sites. One is installed in Villeneuve d'Ascq, in the north of France (VDA). It is an urban site in a topographically flat region. Another instrument is installed in Observatoire de Haute-Provence, located in the southern French Alps (OHP). It is a rural mountainous site. The third instrument is installed in Saint-Denis, Réunion Island (SDR). It is a coastal urban site on a small mountainous island in the southern tropics. The three instruments are affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC) and carry out routine measurements to monitor the spectral solar UV radiation and enable derivation of UV index (UVI). The ground-based UVI values observed at solar noon are compared to similar quantities derived from the Ozone Monitoring Instrument (OMI, onboard the Aura satellite) and the second Global Ozone Monitoring Experiment (GOME-2, onboard the Metop-A satellite) measurements for validation of these satellite-based products. The present study concerns the period 2009–September 2012, date of the implementation of a new OMI processing tool. The new version (v1.3) introduces a correction for absorbing aerosols that were not considered in the old version (v1.2). Both versions of the OMI UVI products were available before September 2012 and are used to assess the improvement of the new processing tool. On average, estimates from satellite instruments always overestimate surface UVI at solar noon. Under cloudless conditions, the satellite-derived estimates of UVI compare satisfactorily with ground-based data: the median relative bias is less than 8 % at VDA and 4 % at SDR for both OMI v1.3 and GOME-2, and about 6 % for OMI v1.3 and 2 % for GOME-2 at OHP. The correlation between satellite-based and ground-based data is better at VDA and OHP (about 0.99) than at SDR (0.96) for both space-borne instruments. For all sky conditions, the median relative biases are much larger, with large dispersion for both instruments at all sites (VDA: about 12 %; OHP: 9 %; SDR: 11 %). Correlation between satellite-based and ground-based data is still better at VDA and OHP (about 0.95) than at SDR (about 0.73) for both satellite instruments. These results are explained considering the time of overpass of the two satellites, which is far from solar noon, preventing a good estimation of the cloud cover necessary for a good modelling of the UVI. Site topography and environment are shown to have a non-significant influence. At VDA and OHP, OMI v1.3 shows a significant improvement with respect to v1.2, which did not account for absorbing aerosols.

A top-down approach of surface carbonyl sulfide exchange by a Mediterranean oak forest ecosystem in southern France

Abstract. The role that soil, foliage, and atmospheric dynamics have on surface carbonyl sulfide (OCS) exchange in a Mediterranean forest ecosystem in southern France (the Oak Observatory at the Observatoire de Haute Provence, O3HP) was investigated in June of 2012 and 2013 with essentially a top-down approach. Atmospheric data suggest that the site is appropriate for estimating gross primary production (GPP) directly from eddy covariance measurements of OCS fluxes, but it is less adequate for scaling net ecosystem exchange (NEE) to GPP from observations of vertical gradients of OCS relative to CO2 during the daytime. Firstly, OCS and carbon dioxide (CO2) diurnal variations and vertical gradients show no net exchange of OCS at night when the carbon fluxes are dominated by ecosystem respiration. This contrasts with other oak woodland ecosystems of a Mediterranean climate, where nocturnal uptake of OCS by soil and/or vegetation has been observed. Since temperature, water, and organic carbon content of soil at the O3HP should favor the uptake of OCS, the lack of nocturnal net uptake would indicate that its gross consumption in soil is compensated for by emission processes that remain to be characterized. Secondly, the uptake of OCS during the photosynthetic period was characterized in two different ways. We measured ozone (O3) deposition velocities and estimated the partitioning of O3 deposition between stomatal and non-stomatal pathways before the start of a joint survey of OCS and O3 surface concentrations. We observed an increasing trend in the relative importance of the stomatal pathway during the morning hours and synchronous steep drops of mixing ratios of OCS (amplitude in the range of 60–100 ppt) and O3 (amplitude in the range of 15–30 ppb) after sunrise and before the break up of the nocturnal boundary layer. The uptake of OCS by plants was also characterized from vertical profiles. However, the time window for calculation of the ecosystem relative uptake (ERU) of OCS, which is a useful tool for partitioning measured NEE, was limited in June 2012 to a few hours after midday. This was due to the disruption of the vertical distribution of OCS by entrainment of OCS rich tropospheric air in the morning and because the vertical gradient of CO2 reverses when it is still light. Moreover, polluted air masses (up to 700 ppt of OCS) produced dramatic variation in atmospheric OCS ∕ CO2 ratios during the daytime in June 2013, further reducing the time window for ERU calculation.

STRONTIUM ABUNDANCES IN COOL DWARF STARS OF GALACTIC THIN AND THICK DISKS

We revise the strontium abundances in FGK stars with metallicities ranging from −1.0 < [Fe/H] < +0.3. The observed stars belong to the substructures of the Galaxy thick and thin discs. The observations were conducted using the1.93 mtelescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle type spectrographs ELODIE and SOPHIE. The values of the Sr abundance were obtained using synthetic spectra using LTE model atmosphere. The comparison of our data with models of chemical evolution was made.

Tentative detection of clear-air turbulence using a ground-based Rayleigh lidar.

Atmospheric gravity waves and turbulence generate small-scale fluctuations of wind, pressure, density, and temperature in the atmosphere. These fluctuations represent a real hazard for commercial aircraft and are known by the generic name of clear-air turbulence (CAT). Numerical weather prediction models do not resolve CAT and therefore provide only a probability of occurrence. A ground-based Rayleigh lidar was designed and implemented to remotely detect and characterize the atmospheric variability induced by turbulence in vertical scales between 40 m and a few hundred meters. Field measurements were performed at Observatoire de Haute-Provence (OHP, France) on 8 December 2008 and 23 June 2009. The estimate of the mean squared amplitude of bidimensional fluctuations of lidar signal showed excess compared to the estimated contribution of the instrumental noise. This excess can be attributed to atmospheric turbulence with a 95% confidence level. During the first night, data from collocated stratosphere-troposphere (ST) radar were available. Altitudes of the turbulent layers detected by the lidar were roughly consistent with those of layers with enhanced radar echo. The derived values of turbulence parameters Cn2 or CT2 were in the range of those published in the literature using ST radar data. However, the detection was at the limit of the instrumental noise and additional measurement campaigns are highly desirable to confirm these initial results. This is to our knowledge the first successful attempt to detect CAT in the free troposphere using an incoherent Rayleigh lidar system. The built lidar device may serve as a test bed for the definition of embarked CAT detection lidar systems aboard airliners.

The SOPHIE search for northern extrasolar planets

Radial velocity planet search surveys of nearby Solar-type stars have shown a strong deficit of brown dwarf companions within $\sim5\,\mathrm{AU}$. There is presently no comprehensive explanation of this lack of brown dwarf companions, therefore, increasing the sample of such objects is crucial to understand their formation and evolution. Based on precise radial velocities obtained using the SOPHIE spectrograph at Observatoire de Haute-Provence we characterise the orbital parameters of $15$ companions to solar-type stars and constrain their true mass using astrometric data from the Hipparcos space mission. The nine companions not shown to be stellar in nature have minimum masses ranging from ~$13$ to $70\,\mathrm{M}_{\mathrm{Jup}}$, and are well distributed across the planet/brown dwarf mass regime, making them an important contribution to the known population of massive companions around solar-type stars. We characterise six companions as stellar in nature with masses ranging from a minimum mass of $76 \pm 4\,\mathrm{M}_{\mathrm{Jup}}$ to a mass of $0.35 \pm 0.03\,\mathrm{M_\odot}$. The orbital parameters of two previously known sub-stellar candidates are improved.

OH reactivity and concentrations of biogenic volatile organic compounds in a Mediterranean forest of downy oak trees

Abstract. Total OH reactivity, defined as the total loss frequency of the hydroxyl radical in the atmosphere, has proved to be an excellent tool to identify the total loading of reactive species in ambient air. High levels of unknown reactivity were found in several forests worldwide and were often higher than at urban sites.Our study presents atmospheric mixing ratios of biogenic compounds and total OH reactivity measured during late spring 2014 at the forest of downy oak trees of the Observatoire de Haute Provence (OHP), France. Air masses were sampled at two heights: 2 m, i.e., inside the canopy, and 10 m, i.e., above the canopy, where the mean canopy height is 5 m.We found that the OH reactivity at the site mainly depended on the main primary biogenic species emitted by the forest, which was isoprene and to a lesser extent by its degradation products and long-lived atmospheric compounds (up to 26 % during daytime). During daytime, no significant missing OH reactivity was reported at the site, either inside or above the canopy. However, during two nights we determined a missing fraction of OH reactivity up to 50 %, possibly due to unmeasured oxidation products. We confirmed that no significant oxidation of the primary species occurred within the canopy; primary compounds emitted by the forest were fast transported to the atmosphere. Finally, the OH reactivity at this site was maximum 69 s−1, which is a high value for a forest characterized by a temperate climate. Observations in various and diverse forests in the Mediterranean region are therefore needed to better constrain the impact of reactive gases over this area.

Imaging polarimetry of comet 73P/Schwassmann–Wachmann 3 main fragments during its 2006 apparition

We have observed the dust ejected by parts of the nucleus (so-called fragments or components) of comet 73P/Schwassmann–Wachmann 3 during seven consecutive nights from 2006, April 27 to May 3 by imaging polarimetry using the 0.8m telescope at OHP (Observatoire de Haute-Provence, France). Three fragments were observed, B and C main fragments on all nights and G fragment on two nights at 24h interval. Fragment C, which almost behaves as a normal comet, presents some night-to-night evolution on polarization maps together with some sunward-jets morphology. Fragment B, as noticed by numerous observers, continues to fragment, with clues to the presence of large secondary fragments, tailward on the intensity images; an increase of activity is noticed on May 2. Jets and fans are observed sunward, with a larger extension in fragment C than in B. Fragment G is fainter and, as fragment B, it continues to fragment. A short sunward jet is detected on the rotational gradient image together with an important tailward structure. The integrated polarization for the two main fragments is typical of polarization of high-Pmax comets. An important evolution is observed from night-to-night on the polarization maps. Fragment C presents, in two nights at 48h interval, a lower polarization in the inner coma, neither observed in the intermediate night nor later. A high polarization is also observed on the two sides of the lower polarization regions. In fragment B, the regions around the secondary fragments have a higher polarization than the surrounding coma, They are easily detected in the treated intensity images. As usually, the polarization increases when the phase angle increases. Numerous observers have found similar chemical compositions for the two main fragments together with differences in their optical properties, suggesting heterogeneities in the physical properties during the aggregation of the original nucleus and/or changes after the ejection of dust particles.

Comparison of Long Term Tropospheric Ozone Trends Measured by Lidar and ECC Ozonesondes from 1991 to 2010 in Southern France

ECC (Electrochemical Concentration Cell) ozonesondes and UV DIAL (Differential Absorption Lidar) measurements have been carried out simultaneously at OHP (Observatoire de Haute Provence, 44°N, 6.7°E, 690 m) since 1991. A unique long-term trend assessment by two different instruments operated routinely at the same location is possible. Air mass trajectories have been calculated for all the ozone observations available at OHP. The bias between the seasonal mean calculated with lidar and ECC ozone vertical profiles for 4 timeperiods of 5 years is 0.6 ppbv in the free troposphere (4-8 km). Larger differences (> 10 ppbv) are explained by the need for clear sky conditions during lidar observations. The measurements of both instruments have been combined to decrease the impact of short-term atmospheric variability on the trend estimate.

Mn abundances in the stars of the Galactic disc with metallicities −1.0 &lt; [Fe/H] &lt; 0.3

In this work we present and discuss the observations of the Mn abundances for 247 FGK dwarfs, located in the Galactic disc with metallicity -1<Fe/H]<+0.3. The observed stars belong to the substructures of the Galaxy thick and thin discs, and to the Hercules stream. The observations were conducted using the 1.93 m telescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle type spectrographs ELODIE and SOPHIE. The abundances were derived under the LTE approximation, with an average error for the [Mn/Fe] ratio of 0.10 dex. For most of the stars in the sample Mn abundances are not available in the literature. We obtain an evolution of [Mn/Fe] ratio with the metallicity [Fe/H] consistent with previous data compilations. In particular, within the metallicity range covered by our stellar sample the [Mn/Fe] ratio is increasing with the increase of metallicity. This due to the contribution to the Galactic chemical evolution of Mn and Fe from thermonuclear supernovae. We confirm the baseline scenario where most of the Mn in the Galactic disc and in the Sun is made by thermonuclear supernovae. In particular, the effective contribution from core-collapse supernovae to the Mn in the Solar system is about 10-20%. However, present uncertainties affecting the production of Mn and Fe in thermonuclear supernovae are limiting the constraining power of the observed [Mn/Fe] trend in the Galactic discs on, e.g., the frequency of different thermonuclear supernovae populations. The different production of these two elements in different types of thermonuclear supernovae needs to be disentangled by the dependence of their relative production on the metallicity of the supernova progenitor.

GHASP: an Hα kinematic survey of spiral galaxies – X. Surface photometry, decompositions and the Tully–Fisher relation in theRcband

We present Rc-band surface photometry for 170 of the 203 galaxies in GHASP, Gassendi H-Alpha survey of SPirals, a sample of late-type galaxies for which high-resolution Fabry-Perot H{\alpha} maps have previously been obtained. Our data set is constructed by new Rc-band observations taken at the Observatoire de Haute-Provence (OHP), supplemented with Sloan Digital Sky Survey (SDSS) archival data, obtained with the purpose of deriving homogeneous photometric profiles and parameters. Our results include Rc-band surface brightness profiles for 170 galaxies and $ugriz$ profiles for 108 of these objects. We catalogue several parameters of general interest for further reference, such as total magnitude, effective radius and isophotal parameters -- magnitude, position angle, ellipticity and inclination. We also perform a structural decomposition of the surface brightness profiles using a multi-component method in order to separate disks from bulges and bars, and to observe the main scaling relations involving luminosities, sizes and maximum velocities. We determine the Rc-band Tully Fisher relation using maximum velocities derived solely from H$\alpha$ rotation curves for a sample of 80 galaxies, resulting in a slope of $-8.1 \pm 0.5$, zero point of $-3.0 \pm 1.0$ and an estimated intrinsic scatter of $0.28 \pm 0.07$. We note that, different from the TF-relation in the near-infrared derived for the same sample, no change in the slope of the relation is seen at the low-mass end (for galaxies with $V_{max} < 125$ km/s). We suggest that this different behaviour of the Tully Fisher relation (with the optical relation being described by a single power-law while the near-infrared by two) may be caused by differences in the stellar mass to light ratio for galaxies with $V_{max} < 125$ km/s.

HAT-P-55b: A Hot Jupiter Transiting a Sun-Like Star11Based on observations obtained with the Hungarian-made Automated Telescope Network. Based in part on radial velocities obtained with the SOPHIE spectrograph mounted on the 1.93-m telescope at Observatoire de Haute-Provence, France. Based in part on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland,

We report the discovery of a new transiting extrasolar planet, HAT-P-55b. The planet orbits a V = 13.207 ± 0.039 sun-like star with a mass of 1.013 ± 0.037 M⊙, a radius of 1.011 ± 0.036 R⊙, and a metallicity of -0.03 ± 0.08. The planet itself is a typical hot Jupiter with a period of 3.5852467 ± 0.0000064 days, a mass of 0.582 ± 0.056 MJ and a radius of 1.182 ± 0.055 RJ. This discovery adds to the increasing sample of transiting planets with measured bulk densities, which is needed to put constraints on models of planetary structure and formation theories.

Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations

The irregular satellites of the giant planets are believed to have been captured during the evolution of the solar system. Knowing their physical parameters, such as size, density, and albedo is important for constraining where they came from and how they were captured. The best way to obtain these parameters are observations in situ by spacecrafts or from stellar occultations by the objects. Both techniques demand that the orbits are well known. We aimed to obtain good astrometric positions of irregular satellites to improve their orbits and ephemeris. We identified and reduced observations of several irregular satellites from three databases containing more than 8000 images obtained between 1992 and 2014 at three sites (Observat\'orio do Pico dos Dias, Observatoire de Haute-Provence, and European Southern Observatory - La Silla). We used the software PRAIA (Platform for Reduction of Astronomical Images Automatically) to make the astrometric reduction of the CCD frames. The UCAC4 catalog represented the International Celestial Reference System in the reductions. Identification of the satellites in the frames was done through their ephemerides as determined from the SPICE/NAIF kernels. Some procedures were followed to overcome missing or incomplete information (coordinates, date), mostly for the older images. We managed to obtain more than 6000 positions for 18 irregular satellites: 12 of Jupiter, 4 of Saturn, 1 of Uranus (Sycorax), and 1 of Neptune (Nereid). For some satellites the number of obtained positions is more than 50\% of what was used in earlier orbital numerical integrations. Comparison of our positions with recent JPL ephemeris suggests there are systematic errors in the orbits for some of the irregular satellites. The most evident case was an error in the inclination of Carme.

Tropospheric nitrogen dioxide column retrieval from ground-based zenith–sky DOAS observations

Abstract. We present an algorithm for retrieving tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) from ground-based zenith–sky (ZS) measurements of scattered sunlight. The method is based on a four-step approach consisting of (1) the differential optical absorption spectroscopy (DOAS) analysis of ZS radiance spectra using a fixed reference spectrum corresponding to low NO2 absorption, (2) the determination of the residual amount in the reference spectrum using a Langley-plot-type method, (3) the removal of the stratospheric content from the daytime total measured slant column based on stratospheric VCDs measured at sunrise and sunset, and simulation of the rapid NO2 diurnal variation, (4) the retrieval of tropospheric VCDs by dividing the resulting tropospheric slant columns by appropriate air mass factors (AMFs). These steps are fully characterized and recommendations are given for each of them. The retrieval algorithm is applied on a ZS data set acquired with a multi-axis (MAX-) DOAS instrument during the Cabauw (51.97° N, 4.93° E, sea level) Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI) held from 10 June to 21 July 2009 in the Netherlands. A median value of 7.9 × 1015 molec cm−2 is found for the retrieved tropospheric NO2 VCDs, with maxima up to 6.0 × 1016 molec cm−2. The error budget assessment indicates that the overall error σTVCD on the column values is less than 28%. In the case of low tropospheric contribution, σTVCD is estimated to be around 39% and is dominated by uncertainties in the determination of the residual amount in the reference spectrum. For strong tropospheric pollution events, σTVCD drops to approximately 22% with the largest uncertainties on the determination of the stratospheric NO2 abundance and tropospheric AMFs. The tropospheric VCD amounts derived from ZS observations are compared to VCDs retrieved from off-axis and direct-sun measurements of the same MAX-DOAS instrument as well as to data from a co-located Système d'Analyse par Observations Zénithales (SAOZ) spectrometer. The retrieved tropospheric VCDs are in good agreement with the different data sets with correlation coefficients and slopes close to or larger than 0.9. The potential of the presented ZS retrieval algorithm is further demonstrated by its successful application on a 2-year data set, acquired at the NDACC (Network for the Detection of Atmospheric Composition Change) station Observatoire de Haute Provence (OHP; Southern France).