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http://inaoe.repositorioinstitucional.mx/jspui/handle/1009/1036| Long-term variability of the optical spectra of NGC 4151: I. Light curves and flux correlations. | |
| VAHRAM CHAVUSHYAN LUIS CARRASCO BAZUA JONATHAN FRANCISCO LEON TAVARES JOSE RAMON VALDES PARRA | |
| Acceso Abierto | |
| Atribución-NoComercial-SinDerivadas | |
| Aims. Results of a long-term spectral monitoring of the active galactic nucleus of NGC 4151 are presented (11 years, from 1996 to 2006). Methods. High quality spectra (S/N>50 in the continuum near Hα and Hα) were obtained in the spectral range ~4000 to 7500 Å, with a resolution between 5 and 15 Å, using the 6-m and the 1-m SAO’s telescopes (Russia), the GHAO’s 2.1-m telescope (Cananea, México), and the OAN-SPM’s 2.1-m telescope (San-Pedro, México). The observed fluxes of the Hα, Hβ, Hγ and HeIIλ4686 emission lines and of the continuum at the observed wavelength 5117Å, were corrected for the position angle, the seeing and the apertura effects. Results. We found that the continuum and line fluxes varied strongly (up to a factor 6) during the monitoring period. The emission was maximum in 1996-1998, and there were two minima, in 2001 and in 2005. As a consequence, the spectral type of the nucleus changed from a Sy1.5 in the maximum activity state to a Sy1.8 in the minimum state. The Hα, Hγ and Heλ4686 fluxes were well correlated with the Hβ flux. The line profiles were strongly variable, showing changes of the blue and red asymmetry. The flux ratios of the blue/red wings and of the blue (or red) wing/core of Hα and Hβ varied differently. We considered three characteristic periods during which the Hβ and Hα profiles were similar: 1996-1999, 2000-2001 and 2002-2006. The line to continuum flux ratios were different; in particular during the first period (1996-2001), the lines were not correlated with the continuum and saturated at high fluxes. In the third period (2002-2006), the Hα and Hβ fluxes were well correlated to the continuum flux, meaning that the ionizing continuum was a good extrapolation of the optical continuum. We thus consider that the values of the time lags – line lagging continuum(0.81_0.81¹•⁵⁵ days for Hα and 0.81_0.81²•¹ days for Hβ) for the third period give a more realistic estimation of the dimensión of the BLR than during the other periods. Moreover, the time lags obtained by binning intervals of three years within the whole monitoring period indicate the permanent presence of a small component of the BLR (0.3-0.7 light days) Conclusions. We discuss the different responses of Hβ and Hα to the continuum during the monitoring period. | |
| Astronomy and Astrophysics | |
| 2008 | |
| Artículo | |
| Inglés | |
| Estudiantes Investigadores Público en general | |
| Shapovalova, A.I., et al., (2008). Long-term variability of the optical spectra of NGC 4151: I. Light curves and flux correlations, Astronomy & Astrophysics, Vol.4856(1):99-111 | |
| ASTRONOMÍA Y ASTROFÍSICA | |
| Versión aceptada | |
| acceptedVersion - Versión aceptada | |
| Aparece en las colecciones: | Artículos de Astrofísica |
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