Miquel Serra-Ricart

Detection of the 2175 Å Extinction Feature at z = 0.83

We determine the extinction curve in the z_l=0.83 lens galaxy of the gravitational lens SBS0909+532 from the wavelength dependence of the flux ratio between the lensed quasar images (z_s=1.38) from 3400 to 9200\AA. It is the first measurement of an extinction curve at a cosmological distance of comparable quality to those obtained within the Galaxy. The extinction curve has a strong 2175\AA feature, a noteworthy fact because it has been weak or non-existent in most estimates of extinction curves outside the Galaxy. The extinction curve is fitted well by a standard

QSO 2237+0305 VR Light Curves from Gravitational LensES International Time Project Optical Monitoring

R_V=2.1\pm0.9

Time Delay in QSO 0957+561 From 1984-1999 Optical Data

Galactic extinction curve. If we assume standard Galactic extinction laws, the estimated dust redshift of

The Rotation Period of C/1995 O1 (Hale-Bopp)

z=0.88\pm0.02

Time Delay of QSO 0957+561 and Cosmological Implications

is in good agreement with the spectroscopic redshift of the lens galaxy. The widespread assumption that SMC extinction curves are more appropriate models for cosmological dust may be incorrect.

BVRI Photometry of QSO 0957+561A, B: Observations, New Reduction Method, and Time Delay

We present VR observations of QSO 2237+0305 conducted by the Gravitational Lensing International Time Project collaboration from 1999 October 1 to 2000 February 3. The observations were made with the 2.56 m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma (Spain). The point-spread function (PSF) fitting method and an adapted version of the ISIS subtraction method have been used to derive the VR light curves of the four components (A-D) of the quasar. The mean errors range in the intervals 0.01-0.04 mag (PSF fitting) and 0.01-0.02 mag (ISIS subtraction), with the faintest component (D) having the largest uncertainties. We address the relatively good agreement between the A and D light curves derived using different filters, photometric techniques, and telescopes. The new VR light curves of component A extend the time coverage of a high-magnification microlensing peak, which was discovered by the OGLE team.

Evolution of a Spiral Jet in the Inner Coma of Comet Hale-Bopp (1995 O1)

Photometric optical data of QSO 0957+561 covering the period 1984-1999 are analyzed to discern between the two values of the time delay (417 and 424 days) mostly accepted in the recent literature. The observations, performed by groups from three different institutions—Princeton University, Harvard-Smithsonian Center for Astrophysics, and Instituto de Astrofisica de Canarias—and including new unpublished 1998-1999 data from the IAC80 Telescope, were obtained in five filters (V, R, I, g, and r). The different light curves have been divided into observational seasons, and two restrictions have been applied to calculate the time delay better: (1) points with a strange photometric behavior have been removed, and (2) data sets without large gaps have been selected. Simulated data were generated to test several numerical methods intended to compute the time delay (ΔτAB). The methods giving the best results—the discrete correlation function, δ2, z-transformed discrete correlation function, and linear interpolation—were then applied to real data. A first analysis of the 23 different time delays derived from each technique shows that ΔτAB must be in the interval 420-424 days. From our statistical study, a most probable value of ΔτAB = 422.6 ± 0.6 days is inferred.

Around-the-Clock Observations of the Q0957+561A,B Gravitationally Lensed Quasar. II. Results for the Second Observing Season

C/1995 O1 (Hale-Bopp) was observed in daylight on 16 days between 1997 April 1 and 1997 April 28, five of which had long time sequences (up to 10 hr of data), using the near infrared CAIN camera on the 1.5 m Carlos Sanchez Telescope at Teide Observatory (Tenerife, Canary Islands, Spain). Three spiral dust jet structures were observed for several almost complete rotations. A nucleus rotation period of 11.34±0.02 hr was determined from two different methods. No variations of the rotation period with time due to precessional effects were found in our data. However, the time sampling of the observations, similar to the suggested spin precession period, prevents us from ascertaining whether such variations exist. We note, though, that the good agreement of our results with the rotation periods at different epochs reported by other groups suggests that if they exist, these variations must be small, hence the rotation cannot be very complex.

Optical studies of the X-ray transient XTE J2123–058 – II. Phase-resolved spectroscopy

We obtain the time delay between the arrival time of the A and B images of the QSO 0957+561. The results of applying two different methods (the discrete cross-correlation function and the dispersion estimation technique) to the observed light curves of the A and B images are presented. The adopted value (time delay) is of ΔτBA = 424 ± 3 days (1 σ). We have used this time delay as well as a recent measurement of the one-dimensional velocity dispersion of the main lensing galaxy (σgal) to estimate H0. Two H0 = H0(ΔτBA, σgal) relations based on different pictures of the lens galaxy, lead to H0 = 64+ 14−15 km s-1 Mpc-1 (2 σ) (softened power-law sphere) and H0 = 66+ 15−14 km s-1 Mpc-1 (2 σ) (King profile plus a point-mass at the center).

The INT Search for Metal-Poor Stars: Spectroscopic Observations and Classification via Artificial Neural Networks

CCD observations of the gravitational lens system Q0957+561A, B in the BVRI bands are presented in this paper. The observations, taken with the 82 cm IAC-80 telescope at Teide Observatory, Spain, were made from the beginning of 1996 February to 1998 July, as part of an ongoing lens-monitoring program. Accurate photometry was obtained by simultaneously fitting a stellar two-dimensional profile on each component by means of DAOPHOT software. This alternative method is equal to and even improves on the results obtained with previous techniques. The final data set is characterized by its high degree of homogeneity, since it was obtained using the same telescope and instrumentation during a period of almost 3 yr. The resulting delay, obtained with a new method, the δ2 test, is of 425 ± 4 days, slightly higher than the value previously accepted (417 days), but concordant with the results obtained by other researchers.