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

Serra-Ricart, Miquel; Oscoz, Alejandro; Sanchís, Teresa; Mediavilla, E.; Goicoechea, Luis Julián; Licandro, Javier; Alcalde, David; Gil-Merino, Rodrigo
Referencia bibliográfica

The Astrophysical Journal, Volume 526, Issue 1, pp. 40-51.

Fecha de publicación:
11
1999
Número de autores
8
Número de autores del IAC
1
Número de citas
34
Número de citas referidas
29
Descripción
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.