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See detailPhotometric accuracy - The impact of extrapolation in differing color-transformation schemes
Manfroid, Jean ULg; Sterken, C.; Gosset, Eric ULg

in Astronomy and Astrophysics (1992), 264

We discuss photometric errors that arise from the use of differing color-transformation schemes when extrapolating outside the range of the standard values that define the system. An example based on data ... [more ▼]

We discuss photometric errors that arise from the use of differing color-transformation schemes when extrapolating outside the range of the standard values that define the system. An example based on data from the Long-Term Photometry of Variables project (LTPV) at ESO is analyzed. Practically, the extrapolation errors are most evident as systematic brightness jumps of some program stars, seen when monitored over several observing runs. Conclusions are drawn about the choice of standard stars in the Stromgren system. [less ▲]

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See detailA photometric and spectroscopic investigation of star formation in the very young open cluster NGC 6383
Rauw, Grégor ULg; Manfroid, Jean ULg; De Becker, Michaël ULg

in Astronomy and Astrophysics (2010), 511

Context. The very young open cluster NGC 6383 centered on the O-star binary HD 159176 is an interesting place for studying the impact of early-type stars with strong radiation fields and powerful winds on ... [more ▼]

Context. The very young open cluster NGC 6383 centered on the O-star binary HD 159176 is an interesting place for studying the impact of early-type stars with strong radiation fields and powerful winds on the formation processes of low-mass stars. <BR /> Aims: To investigate this process, it is necessary to determine the characteristics (age, presence, or absence of circumstellar material) of the population of low-mass pre-main-sequence (PMS) stars in the cluster. <BR /> Methods: We obtained deep UBV(RI)[SUB]c[/SUB] Hα photometric data of the entire cluster as well as medium-resolution optical spectroscopy of a subsample of X-ray selected objects. <BR /> Results: Our spectroscopic data reveal only very weak Hα emission lines in a few X-ray selected PMS candidates. We photometrically identify a number of Hα emission candidates but their cluster membership is uncertain. We find that the fainter objects in the field of view have a wide range of extinction (up to A[SUB]V[/SUB] = 20), one X-ray selected OB star having A[SUB]V[/SUB] â 8. <BR /> Conclusions: Our investigation uncovers a population of PMS stars in NGC 6383 that are probably coeval with HD 159176. In addition, we detect a population of reddened objects that are probably located at different depths within the natal molecular cloud of the cluster. Finally, we identify a rather complex spatial distribution of Hα emitters, which is probably indicative of a severe contamination by foreground and background stars. Based on observations collected at the European Southern Observatory (ESO, La Silla, Chile).Table 2 is only available in electronic form at the CDS via anonymous ftp cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/511/A25">http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/511/A25</A> [less ▲]

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See detailA photometric classification of Wolf-Rayet stars
Vreux, Jean-Marie ULg; Manfroid, Jean ULg; Royer, P.

in Liege International Astrophysical Colloquia (1996)

Not Available

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See detailPhotometric measurements of the O2 U.V. nightglow
Gérard, Jean-Claude ULg

in Planetary and Space Science (1975), 23

The O2 Herzberg system in the night airglow was measured in the wavelength range 2400 to 3100 A by the S2/68 UV telescope aboard the ESRO TD-1 satellite. The statistical latitudinal variations of the ... [more ▼]

The O2 Herzberg system in the night airglow was measured in the wavelength range 2400 to 3100 A by the S2/68 UV telescope aboard the ESRO TD-1 satellite. The statistical latitudinal variations of the slant emissional rates are analysed; auroral contamination by other emissions was eliminated from the data by monitoring the light levels in the other channels of the experiment. The slant emission rate varies from 3.5 to 15 kR, indicating an irregular structure of the atomic oxygen near the turbopause. A maximum average intensity occurrs near the tropics in the winter hemisphere. The observed emission rate is accounted for quantitatively by the three-body recombination of atmospheric oxygen using an estimated 20 per cent production efficiency for the A(3) sigma state, if quenching by N2 occurrs at the rate approximated from the relative statistical weight of the A state. [less ▲]

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See detailA photometric method to study the Wolf-Rayet content of compact H II regions in nearby galaxies
Royer, P.; Vreux, Jean-Marie ULg; Manfroid, Jean ULg

in The Magellanic Clouds and Other Dwarf Galaxies (1998)

Not Available

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See detailPhotometric Mode Identification in the Two Doradus Stars HD 12901 and HD 48501
Aerts, C.; Cuypers, J.; Dupret, Marc-Antoine ULg et al

in Asteroseismology Across the HR Diagram (2003)

Not Available

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See detailA photometric mode identification method, including an improved non-adiabatic treatment of the atmosphere
Dupret, Marc-Antoine ULg; De Ridder, J.; De Cat, P. et al

in Astronomy and Astrophysics (2003), 398

We present an improved version of the method of photometric mode identification of Heynderickx et al. (\cite{hey}). Our new version is based on the inclusion of precise non-adiabatic eigenfunctions ... [more ▼]

We present an improved version of the method of photometric mode identification of Heynderickx et al. (\cite{hey}). Our new version is based on the inclusion of precise non-adiabatic eigenfunctions determined in the outer stellar atmosphere according to the formalism recently proposed by Dupret et al. (\cite{dup}). Our improved photometric mode identification technique is therefore no longer dependent on ad hoc parameters for the non-adiabatic effects. It contains the complete physical conditions of the outer atmosphere of the star, provided that rotation does not play a key role. We apply our method to the two slowly pulsating B stars HD 74560 and HD 138764 and to the beta Cephei star EN (16) Lac. Besides identifying the degree l of the pulsating stars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on parameters such as the metallicity and the mixing-length parameter alpha (a procedure we label non-adiabatic asteroseismology). The non-adiabatic eigenfunctions needed for the mode identification are available upon request from the authors. [less ▲]

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See detailPhotometric monitoring (1987 to 1994) of the gravitational lens candidate UM 425.
Courbin, F.; Magain, Pierre ULg; Remy, M. et al

in Astronomy and Astrophysics (1995), 303

We present the results of a 7 year long photometric monitoring of two components (A and B) of UM 425, thought to be images, separated by 6.5", of the same z=1.47 quasar. These components have been imaged ... [more ▼]

We present the results of a 7 year long photometric monitoring of two components (A and B) of UM 425, thought to be images, separated by 6.5", of the same z=1.47 quasar. These components have been imaged through an R filter in order to obtain their light curves. The photometry was obtained by simultaneously fitting a stellar two-dimensional profile on each component. The brightest image (component A, m_R_=15.7) shows a slow and smooth increase in brightness of 0.2 magnitude in seven years, while the faintest one (component B, m_R_=20.1) displays an outburst of 0.4 magnitude which lasts approximately two years. The variation of component B may be interpreted in two ways, assuming UM 425 is gravitationally lensed. If it is due to an intrinsic variation of the quasar, we derive a lower limit of 3 years on the time delay from the fact that it is not observed in component A. On the other hand, if it is a microlensing "High Amplification Event", we estimate the size of the source to be ~10^-3^pc, in agreement with standard models of AGNs. These observations are consistent with the gravitational lens interpretation of the object. Furthermore, all the CCD frames obtained under the best seeing conditions have been co-added, in an attempt to detect the deflector. The final R image reveals a rich field of faint galaxies in the magnitude range m_R_~22-24. No obvious deflector, nor any system of arcs or arclets is detected, down to a limiting magnitude of m_R_~24. [less ▲]

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See detailPhotometric monitoring of the doubly imaged quasar UM 673: possible evidence for chromatic microlensing
Nakos, Theodoros; Courbin, F.; Poels, Joël ULg et al

in Astronomy and Astrophysics (2005), 441

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673). The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i ... [more ▼]

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673). The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i-band (October 1998-September 1999) and in the Johnson V-band (October 1998 to December 2001), were analyzed using three different photometric methods. The light-curves obtained with all methods show variations, with a peak-to-peak amplitude of 0.14 mag in V. Although it was not possible to measure the time delay between the two lensed QSO images, the brighter component displays possible evidence for microlensing: it becomes bluer as it gets brighter, as expected under the assumption of differential magnification of a quasar accretion disk. [less ▲]

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See detailPhotometric monitoring of Wolf-Rayet stars: Strömgren uvby and narrow-band photometry
Gosset, Eric ULg; Rauw, Grégor ULg; Manfroid, Jean ULg et al

in NATO ASIC Proc. 436: The Impact of Long-Term Monitoring on Variable Star Research: Astrophysics (1994)

Not Available

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See detailPhotometric multi-site campaign on the open cluster NGC 884. I. Detection of the variable stars
Saesen, S.; Carrier, F.; Pigulski, A. et al

in Astronomy and Astrophysics (2010), 515

Context. Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further ... [more ▼]

Context. Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. <BR /> Aims: To improve our comprehension of the β Cep stars, we studied the young open cluster NGC 884 to discover new B-type pulsators, besides the two known β Cep stars, and other variable stars. <BR /> Methods: An extensive multi-site campaign was set up to gather accurate CCD photometry time series in four filters (U, B, V, I) of a field of NGC 884. Fifteen different instruments collected almost 77 500 CCD images in 1286 h. The images were calibrated and reduced to transform the CCD frames into interpretable differential light curves. Various variability indicators and frequency analyses were applied to detect variable stars in the field. Absolute photometry was taken to deduce some general cluster and stellar properties. <BR /> Results: We achieved an accuracy for the brightest stars of 5.7 mmag in V, 6.9 mmag in B, 5.0 mmag in I and 5.3 mmag in U. The noise level in the amplitude spectra is 50 μmag in the V band. Our campaign confirms the previously known pulsators, and we report more than one hundred new multi- and mono-periodic B-, A- and F-type stars. Their interpretation in terms of classical instability domains is not straightforward, pointing to imperfections in theoretical instability computations. In addition, we have discovered six new eclipsing binaries and four candidates as well as other irregular variable stars in the observed field. The photometric data of the variable stars are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A16">http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A16</A> [less ▲]

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See detailPhotometric observations of 1978CA and 1978DA
Surdej, Jean ULg; Surdej, Anna ULg

in The Messenger (1978), 13

UBV photometric observations of the earth-crossing asteroid 1978 CA and the Mars-crosser 1978 DA are reported. Light curves are plotted which indicate that 1978 CA has a rotation period of approximately 3 ... [more ▼]

UBV photometric observations of the earth-crossing asteroid 1978 CA and the Mars-crosser 1978 DA are reported. Light curves are plotted which indicate that 1978 CA has a rotation period of approximately 3 hr 45 min and that 1978 DA rotates about its axis much more slowly than 1978 CA. The following color indices are determined: (B-V) of approximately 0.90 and (U-B) of about 0.48 for 1978 CA and (B-V) = 0.83 and (U-B) = 0.41 for 1978 DA. A model that may explain the observed smooth and nearly symmetric light curve of 1978 CA is briefly discussed. [less ▲]

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See detailPhotometric observations of HD 50169.
Heck, A.; Maitzen, H. M.; Renson, Pierre ULg

in Astronomy and Astrophysics (1977), 54

Abstract image available at: http://adsabs.harvard.edu/abs/1977A&A....54..635H

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See detailPhotometric Observations of WR78 = HD 151932
Magain, Pierre ULg; Vreux, Jean-Marie ULg; Manfroid, Jean ULg

in Information Bulletin on Variable Stars (1987), 3022

Not Available

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See detailA photometric study of southern Ap stars having right ascensions on the order of 12 h
Manfroid, Jean ULg; Renson, Pierre ULg

in Astronomy and Astrophysics. Supplement Series (1983), 51

From uvby measurements periods have been deduced for the Ap stars 25 Sex, HR 4327, β Hya, HD 112381, HR 4965, HR 5158, HR 5269, and HD 125630. The star HR 4109 (Sr?) remained constant during an interval ... [more ▼]

From uvby measurements periods have been deduced for the Ap stars 25 Sex, HR 4327, β Hya, HD 112381, HR 4965, HR 5158, HR 5269, and HD 125630. The star HR 4109 (Sr?) remained constant during an interval of 23 d; the period is perhaps very long, or if HR 4109 actually does not vary, possibly it is not an Ap star. The observed variation for l Cen (Mn) was too weak to deduce a period. The variation range of HD 112381 (SiCr) is nearly as small as that of l Cen. The v and y variations for HD 125630 (SiCrSr), which are double-waved and nearly opposite to one another, have ranges among the largest known for Ap stars; the c[SUB]1[/SUB] range is also exceptionally large. For some Ap stars the variation curves show a dip of short duration in the four colours, and for a few stars a second one appears at a phase-interval of P/2. The nature of this phenomenon is discussed. [less ▲]

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See detailA photometric study of the bright cloud B in Sagittarius. VII - 1165 new variable stars and 65 diffuse objects
Terzan, A.; Gosset, Eric ULg

in Astronomy and Astrophysics. Supplement Series (1991), 90

A field in the Sagittarian bright cloud in the direction of the Galactic center is investigated by means of the B, V, and R Schmidt plates at the ESO, and 1165 variable stars are reported. The position, R ... [more ▼]

A field in the Sagittarian bright cloud in the direction of the Galactic center is investigated by means of the B, V, and R Schmidt plates at the ESO, and 1165 variable stars are reported. The position, R magnitudes, epochs, and amplitudes of variation are given for each star, and the surface density per square degree of variable stars increases from 1.7 to 65. The number of variables in the present field is similar to that for field A, and variables of type L and/or M are more densely numerous toward the center of the Galaxy than at other locations. Of the objects listed, 65 are given with potential classifications based on morphological data from the B and R Schmidt plates. The preliminary observations suggest a success rate of 42 percent on the precise prediction of the object types. [less ▲]

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See detailA photometric study of the Carina nebula region around WR 22
Kumar, Brajesh ULg; Manfroid, Jean ULg; Gosset, Eric ULg et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

We performed the first photometric observations of a field situated around WR 22 in the Carina nebula region. We present and discuss the preliminary results of the study.

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See detailA Photometric Study of the Hot Exoplanet WASP-19b
Lendl, M.; Gillon, Michaël ULg; Queloz, D. et al

in Astronomy and Astrophysics (2013), 552

Context. The sample of hot Jupiters that have been studied in great detail is still growing. In particular, when the planet transits its host star, it is possible to measure the planetary radius and the ... [more ▼]

Context. The sample of hot Jupiters that have been studied in great detail is still growing. In particular, when the planet transits its host star, it is possible to measure the planetary radius and the planet mass (with radial velocity data). For the study of planetary atmospheres, it is essential to obtain transit and occultation measurements at multiple wavelengths. Aims: We aim to characterize the transiting hot Jupiter WASP-19b by deriving accurate and precise planetary parameters from a dedicated observing campaign of transits and occultations. Methods: We have obtained a total of 14 transit lightcurves in the r'-Gunn, I-Cousins, z'-Gunn, and I + z' filters and 10 occultation lightcurves in z'-Gunn using EulerCam on the Euler-Swiss telescope and TRAPPIST. We also obtained one lightcurve through the narrow-band NB1190 filter of HAWK-I on the VLT measuring an occultation at 1.19 μm. We performed a global MCMC analysis of all new data, together with some archive data in order to refine the planetary parameters and to measure the occultation depths in z'-band and at 1.19 μm. Results: We measure a planetary radius of Rp = 1.376 ± 0.046 RJ, a planetary mass of Mp = 1.165 ± 0.068 MJ, and find a very low eccentricity of e = 0.0077-0.0032+0.0068, compatible with a circular orbit. We have detected the z'-band occultation at 3σ significance and measure it to be δFocc,z' = 352 ± 116 ppm, more than a factor of 2 smaller than previously published. The occultation at 1.19 μm is only marginally constrained at δFocc,NB1190 = 1711-726+745 ppm. Conclusions: We show that the detection of occultations in the visible range is within reach, even for 1 m class telescopes if a considerable number of individual events are observed. Our results suggest an oxygen-dominated atmosphere of WASP-19b, making the planet an interesting test case for oxygen-rich planets without temperature inversion. [less ▲]

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See detailPhotometric study of the lensed quasar HE0435-1223
Ricci, Davide ULg

Scientific conference (2010, February 11)

We present the preliminary results of a systematic multi-filter photometric observations of HE0435, carried with the Danish 1.54m telescope at the La Silla Observatory. We performed 2 seasons of ... [more ▼]

We present the preliminary results of a systematic multi-filter photometric observations of HE0435, carried with the Danish 1.54m telescope at the La Silla Observatory. We performed 2 seasons of monitoring in VRI spectral bands and we are reducing the data using an integrated C++ software developed in our team. [less ▲]

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See detailPhotometric variability of barium stars
Jorissen, A.; Manfroid, Jean ULg; Sterken, C.

in Astronomy and Astrophysics (1992), 253

Results are presented on uvby observations for up to 4 years of 19 southern barium stars. During the observation period, only two of the stars, HD 121447 and HD 46407, showed significant light variations ... [more ▼]

Results are presented on uvby observations for up to 4 years of 19 southern barium stars. During the observation period, only two of the stars, HD 121447 and HD 46407, showed significant light variations. These variables are the stars among the sample with the shortest orbital periods. In the case of HD 46407, evidence for eclipses was also found. It is noted that the evidence of varying phase shifts between the photometric eclipse and the spectroscopic ephemeris based on McClure and Woodsworth's (1990) orbital parameters makes it unlikely that the eclipsed light arises directly from the stellar companion of the barium star. It is also suggested that the flickering displayed by the reddest barium stars is a generic property of all red stars, because it was also observed for the comparison stars HD 204139 and HD 90677. [less ▲]

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