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Astron. Astrophys. 352, L11-L16 (1999)

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Letter to the Editor

Observations of the host galaxies of the BL Lacertae objects H 0414+009 and OJ 287 with FORS1 at VLT-UT1 *

J. Heidt 1, K. Nilsson 2, I. Appenzeller 1, K. Jäger 3, W. Seifert 1, T. Szeifert 1,4, W. Gässler 5, R. Häfner 5, W. Hummel 5, B. Muschielok 5, H. Nicklas 3 and O. Stahl 1

1 Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany
2 Tuorla Observatory, 21500 Piikkiö, Finland
3 Universitäts-Sternwarte Göttingen, Geismarlandstrasse 11, 37083 Göttingen, Germany
4 ESO Santiago, Alonso de Cordova 3107, Santiago 19, Chile
5 Universitäts-Sternwarte München, Scheinerstrasse 1, 81679 München, Germany

Received 11 August 1999 / Accepted 11 October 1999

Abstract

We present imaging of the host galaxies of H 0414+009 and OJ 287 taken during the commissioning phases of FORS1 at the VLT-UT1. The host galaxy of H 0414+009 is well resolved in R and I, and marginally resolved in B. Based on our 2-dimensional modelling, it is a large and very luminous elliptical galaxy ([FORMULA] = -24.6, [FORMULA] = 35 kpc) with colours commonly found in elliptical galaxies (B-R [FORMULA] 1.45 and R-I [FORMULA] 0.45). The results are consistent with previous findings.

The host galaxy of OJ 287 is marginally resolved. A de Vaucouleurs profile is slightly preferred over a disk-type profile. If true, the host galaxy is luminous ([FORMULA] = -23.4), compact ([FORMULA] = 4.4 kpc) and has a small offset to the south with respect to the active nucleus. This is consistent with the results obtained by Sillanpää et al. (1999), but different to the findings by Wurtz et al. (1996) and Yanny et al. (1997).

The analysis of the marginally resolved host galaxies was complicated by a point spread function (PSF) varying across the field. Consequently, better results were obtained when using a PSF which varies with field position as compared to a constant PSF. This is possible as long as a sufficient number of stars is present on the images. Masking the central regions mostly affected by the PSF errors may also improve the results. Based on our experience we describe precaution which has to be taken for FORS1 observations and subsequent analysis of marginally resolved targets such as AGN host galaxies or planetary nebulae around young stellar objects.

Key words: methods: data analysis – galaxies: active – galaxies: BL Lacertae objects: individual: H 0414+009 – galaxies: BL Lacertae objects: individual: OJ 287 – galaxies: photometry

* Based on observations made with the VLT-UT1, operated on Cerro Paranal (Chile) by the European Southern Observatory

Send offprint requests to: J. Heidt (jheidt@lsw.uni-heidelberg.de)

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© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999
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