The aim of this study is to determine the effects of red mullet gillnets that are commonly used in Turkish waters on the sustainability of non-target fish species. For this purpose, surveys were ...realized with 18 - 20 - 22 mm nominal bar length red mullet gillnets between December 2008 and May 2010 along the north Aegean Sea coasts (5-30 m). SELECT method was used with five different models (Normal location, normal scale, log-normal, gamma and bi-modal) for evaluating selectivity parameters of non-target fish species. Selectivity models were determined as bi-modal for Serranus scriba and Symphodus tinca, log normal for Scorpaena porcus and Spicara maena and gamma for Pagellus acarne. Optimum catch lengths and spread values and selectivity curves were given for 5 species. Results showed that use of a larger mesh size over the 22mm mesh is important for ensuring stock sustainability of the non-target fish species.
In this study, gillnet selectivity of saddled seabream (Oblada melanura), common two-banded seabream (Diplodus vulgaris), annular seabream (Diplodus annularis) and Mediterranean horse mackerel ...(Trachurus mediterraneus) which were caught by bogue gillnets with 20, 22, 23 and 25 mm mesh size (nominal bar lenght) have been determined. Fishing trials were carried out in North Aegean Sea from March 2008 to February 2010. Selectivity parameters were estimated using the Select method. Most suitable selectivity models were calculated as log-normal for saddled seabream (O. melanura) and annular seabream (D. annularis), bi-modal for Mediterranean horse mackerel (T. mediterraneus) and common two-banded seabream (D. vulgaris). Optimum catch lengths for 20, 22, 23 and 25 mm mesh size were 11.15, 12.27, 12.83 ve 13.94 cm for annular seabream (D. annularis), 11.26, 12.39, 12.95 and 14.08 cm for common two-banded seabream (D. vulgaris), 15.3, 16.83, 17.59 and 19.12 cm for saddled seabream (O. melanura), and 26.68, 29.35, 30.68 and 33.35 cm for Mediterranean horse mackerel (T. mediterraneus), respectively. These findings may help to understand that using higher than 23 mm stretched mesh size with gillnets which have been used for commercial bogue fisheries around north Aegean Sea is important for sustainability of fisheries.
A single male specimen of the royal flagfin (Aulopus filamentosus), 369 mm total length was caught with the longline from the Gokceada Island, north Aegean Sea (Turkey). This report constitutes the ...reconfirmed occurrence which gives precise locality information from the Turkish waters and this record reflects northernmost expansion of this species in the Aegean Sea.
ASTEP 400, the main instrument of the ASTEP (Antarctica Search for Transiting ExoPlanets) programme, is a 40 cm telescope, designed to withstand the harsh conditions in Antarctica, achieving a ...photometric accuracy of a fraction of millimagnitude on hourly time-scales for planet-hosting southern bright (R ∼ 12 mag) stars. We review the performances of this instrument, describe its operating conditions, and present results from the analysis of observations obtained during its first three years (2010–2012) of operation, before its repatriation in 2014. During this time, we observed a total of 22 stellar fields (1° × 1° field of view). Each field, in which we measured stars up to magnitude R = 18 mag, was observed continuously during ∼7 to ∼30 d. More than 200 000 frames were recorded and 310 000 stars processed, using an implementation of the optimal image subtraction photometry algorithm. We found 43 planetary transit candidates. 20 of these candidates were observed using spectroscopic follow-ups including four targets classified as good planet candidates. Our results demonstrate that accurate near-continuous photometric observations are achievable from the Concordia station at Dome C in Antarctica, even if we were not able to reach the nominal photometric precision of the instrument. We conducted a correlation analysis between the rms noise and a large number of external parameters and found that source of the ∼1 mmag correlated noise is not obvious and does not depend on a single parameter. However, our analysis provided some hints and guidance to increase the photometric accuracy of the instrument. These improvements should equip any future telescope operating in Antarctica.
Context. Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. Aims.We developed ...instruments to assess the quality of this site for photometry in the visible and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. Methods. Here, we present the full analysis of four winters of data collected with ASTEP South, a 10 cm refractor pointing continuously toward the celestial south pole. We improved the instrument over the years and developed specific data reduction methods. Results. We achieved nearly continuous observations over the winters. We measure an average sky background of 20 mag arcsec−2 in the 579–642 nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric 67.1 ± 4.2% of the time and veiled 21.8 ± 2.0% of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of σ Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. Conclusion. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general.
Context. The SPHERE “planet finder” is an extreme adaptive optics (AO) instrument for high resolution and high contrast observations at the Very Large Telescope (VLT). We describe the Zurich Imaging ...Polarimeter (ZIMPOL), the visual focal plane subsystem of SPHERE, which pushes the limits of current AO systems to shorter wavelengths, higher spatial resolution, and much improved polarimetric performance. Aims. We present a detailed characterization of SPHERE/ZIMPOL which should be useful for an optimal planning of observations and for improving the data reduction and calibration. We aim to provide new benchmarks for the performance of high contrast instruments, in particular for polarimetric differential imaging. Methods. We have analyzed SPHERE/ZIMPOL point spread functions (PSFs) and measure the normalized peak surface brightness, the encircled energy, and the full width half maximum (FWHM) for different wavelengths, atmospheric conditions, star brightness, and instrument modes. Coronagraphic images are described and the peak flux attenuation and the off-axis flux transmission are determined. Simultaneous images of the coronagraphic focal plane and the pupil plane are analyzed and the suppression of the diffraction rings by the pupil stop is investigated. We compared the performance at small separation for different coronagraphs with tests for the binary α Hyi with a separation of 92 mas and a contrast of Δm ≈ 6m. For the polarimetric mode we made the instrument calibrations using zero polarization and high polarization standard stars and here we give a recipe for the absolute calibration of polarimetric data. The data show small (< 1 mas) but disturbing differential polarimetric beam shifts, which can be explained as Goos-Hähnchen shifts from the inclined mirrors, and we discuss how to correct this effect. The polarimetric sensitivity is investigated with non-coronagraphic and deep, coronagraphic observations of the dust scattering around the symbiotic Mira variable R Aqr. Results. SPHERE/ZIMPOL reaches routinely an angular resolution (FWHM) of 22−28 mas, and a normalized peak surface brightness of SB0 − mstar ≈ −6.5m arcsec−2 for the V-, R- and I-band. The AO performance is worse for mediocre ≳1.0″ seeing conditions, faint stars mR ≳ 9m, or in the presence of the “low wind” effect (telescope seeing). The coronagraphs are effective in attenuating the PSF peak by factors of > 100, and the suppression of the diffracted light improves the contrast performance by a factor of approximately two in the separation range 0.06″−0.20″. The polarimetric sensitivity is Δp < 0.01% and the polarization zero point can be calibrated to better than Δp ≈ 0.1%. The contrast limits for differential polarimetric imaging for the 400 s I-band data of R Aqr at a separation of ρ = 0.86″ are for the surface brightness contrast SBpol( ρ)−mstar ≈ 8m arcsec−2 and for the point source contrast mpol( ρ)−mstar ≈ 15m and much lower limits are achievable with deeper observations. Conclusions. SPHERE/ZIMPOL achieves imaging performances in the visual range with unprecedented characteristics, in particular very high spatial resolution and very high polarimetric contrast. This instrument opens up many new research opportunities for the detailed investigation of circumstellar dust, in scattered and therefore polarized light, for the investigation of faint companions, and for the mapping of circumstellar Hα emission.
Context
. The SPHERE “planet finder” is an extreme adaptive optics (AO) instrument for high resolution and high contrast observations at the Very Large Telescope (VLT). We describe the Zurich Imaging ...Polarimeter (ZIMPOL), the visual focal plane subsystem of SPHERE, which pushes the limits of current AO systems to shorter wavelengths, higher spatial resolution, and much improved polarimetric performance.
Aims
. We present a detailed characterization of SPHERE/ZIMPOL which should be useful for an optimal planning of observations and for improving the data reduction and calibration. We aim to provide new benchmarks for the performance of high contrast instruments, in particular for polarimetric differential imaging.
Methods
. We have analyzed SPHERE/ZIMPOL point spread functions (PSFs) and measure the normalized peak surface brightness, the encircled energy, and the full width half maximum (FWHM) for different wavelengths, atmospheric conditions, star brightness, and instrument modes. Coronagraphic images are described and the peak flux attenuation and the off-axis flux transmission are determined. Simultaneous images of the coronagraphic focal plane and the pupil plane are analyzed and the suppression of the diffraction rings by the pupil stop is investigated. We compared the performance at small separation for different coronagraphs with tests for the binary
α
Hyi with a separation of 92 mas and a contrast of Δ
m
≈ 6
m
. For the polarimetric mode we made the instrument calibrations using zero polarization and high polarization standard stars and here we give a recipe for the absolute calibration of polarimetric data. The data show small (< 1 mas) but disturbing differential polarimetric beam shifts, which can be explained as Goos-Hähnchen shifts from the inclined mirrors, and we discuss how to correct this effect. The polarimetric sensitivity is investigated with non-coronagraphic and deep, coronagraphic observations of the dust scattering around the symbiotic Mira variable R Aqr.
Results
. SPHERE/ZIMPOL reaches routinely an angular resolution (FWHM) of 22−28 mas, and a normalized peak surface brightness of SB
0
−
m
star
≈ −6.5
m
arcsec
−2
for the
V
-,
R
- and
I
-band. The AO performance is worse for mediocre ≳1.0″ seeing conditions, faint stars
m
R
≳ 9
m
, or in the presence of the “low wind” effect (telescope seeing). The coronagraphs are effective in attenuating the PSF peak by factors of > 100, and the suppression of the diffracted light improves the contrast performance by a factor of approximately two in the separation range 0.06″−0.20″. The polarimetric sensitivity is Δ
p
< 0.01% and the polarization zero point can be calibrated to better than Δ
p
≈ 0.1%. The contrast limits for differential polarimetric imaging for the 400 s
I
-band data of R Aqr at a separation of
ρ
= 0.86″ are for the surface brightness contrast SB
pol
(
ρ
)−
m
star
≈ 8
m
arcsec
−2
and for the point source contrast
m
pol
(
ρ
)−
m
star
≈ 15
m
and much lower limits are achievable with deeper observations.
Conclusions
. SPHERE/ZIMPOL achieves imaging performances in the visual range with unprecedented characteristics, in particular very high spatial resolution and very high polarimetric contrast. This instrument opens up many new research opportunities for the detailed investigation of circumstellar dust, in scattered and therefore polarized light, for the investigation of faint companions, and for the mapping of circumstellar H
α
emission.
Aims. The Antarctica Search for Transiting ExoPlanets (ASTEP) program was originally aimed at probing the quality of the Dome C, Antarctica for the discovery and characterization of exoplanets by ...photometry. In the first year of operation of the 40 cm ASTEP 400 telescope (austral winter 2010), we targeted the known transiting planet WASP-19b in order to try to detect its secondary transits in the visible. This is made possible by the excellent sub-millimagnitude precision of the binned data. Methods. The WASP-19 system was observed during 24 nights in May 2010. Once brought back from Antarctica, the data were processed using various methods, and the best results were with an implementation of the optimal image subtraction (OIS) algorithm. Results. The photometric variability level due to starspots is about 1.8% (peak-to-peak), in line with the SuperWASP data from 2007 (1.4%) and higher than in 2008 (0.07%). We find a rotation period of WASP-19 of 10.7 ± 0.5 days, in agreement with the SuperWASP determination of 10.5 ± 0.2 days. Theoretical models show that this can only be explained if tidal dissipation in the star is weak, i.e. the tidal dissipation factor Q'★ > 3×107. Separately, we find evidence of a secondary eclipse of depth 390 ± 190 ppm with a 2.0σ significance, a phase that is consistent with a circular orbit and a 3% false positive probability. Given the wavelength range of the observations (420 to 950 nm), the secondary transit depth translates into a day-side brightness temperature of 2690-220+150 K, in line with measurements in the z′ and K bands. The day-side emission observed in the visible could be due either to thermal emission of an extremely hot day side with very little redistribution of heat to the night side or to direct reflection of stellar light with a maximum geometrical albedo Ag = 0.27 ± 0.13. We also report a low-frequency oscillation in phase at the planet orbital period, but with a lower limit amplitude that could not be attributed to the planet phase alone and that was possibly contaminated with residual lightcurve trends. Conclusions. This first evidence of a secondary eclipse in the visible from the ground demonstrates the high potential of Dome C, Antarctica, for continuous photometric observations of stars with exoplanets. These continuous observations are required to understand star-planet interactions and the dynamical properties of exoplanetary atmospheres.
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