Studying the Infrared Variability in Seyfert ~1 Galaxies

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Session 59 -- Low Luminosity AGNs and Active Galaxies
Display presentation, Thursday, 2, 1994, 9:20-6:30

[59.12] Studying the Infrared Variability in Seyfert ~1 Galaxies

S.Josephine Chan (NCU/MPG), Wei-Hsin Sun (NCU)

\def\iras {{$IRAS~$}} \def\app {{$\approx~$}}

We present the preliminary results on the study of infrared variability of a sample of 10 Seyfert~1 galaxies. The sample was selected based on the following criteria: i) they are bright ($m_{V}<15.2$), ii) they have ``big blue bumps'', and iii) they show detectable flux variabilities in the UV-Optical spectral regions.

The near-IR data were collected from the published literature while the mid-IR flux points were obtained from the IRAS survey data. Aperture effect, galactic reddening, and internal reddening have been corrected. A strong correlation was found among the variabilities of near-IR magnitudes. The correlation can be described by a parabola which is obtained from the least square fitting technique, the Lybannon algorithm. Similar near-IR color variabilities are found for each galaxy in the sample. The variable ranges of J-H and H-K are both $\sim0.7-1.0$ in the JHK color-color diagram, while the range of H-K is $\sim0.7-1.0$ and K-L is $\sim1.1-1.7$ in the HKL color-color diagram. This suggests that the near-IR emission in these galaxies are from similar origin. The slope variability is weakly correlated with the flux variability.

We defined an IRAS variability index which can be considered as a semi-quantitative measure of the minimum degree of variability at a particular wavelength. The IRAS variability indices of ESO~141-G55, Mkn~841, ZW~II136, and NGC~6814 are higher than 3. The variability amplitudes of the sample objects are smaller than that in the UV, Optical, and near-IR. The locations of the color-variability boxes of the sample objects are not as uniform as in the near-IR, which indicates that the origins of the mid-IR and near-IR emissions may be different.

The survey data used in this analysis are provided by IPAC. This work is supported by the National Science Council in Taiwan, ROC, through the grant NSC~83-0208-M-008-015.

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