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The Landessternwarte Faint Object Spectrograph and Camera



The Landessternwarte Faint Object Spectrograph and Camera (LFOSC) is a focal reducer camera that was constructed at the Landessternwarte Heidelberg, Germany. The instrument is attached to the Cassegrain focus of the telescope and allows direct CCD imaging, filter photometry, and multi-object spectroscopy. It is equipped with an EEV P8603 CCD detector (385X578 pixels, 22m linear pixel size). With a 10' X 6' field of view the image scale is 1"/pixel.

The LFOSC was installed at the Guillermo Haro Observatory (GHO) through the  project "Optical  Identification of ROSAT X-ray sources" started in 1991. The description of the project and  LFOSC can be found in  Zickgraf et al. (1997).

For direct imaging it is possible to use Johnson B,V , Cousins R,I and H filters. A limiting magnitude of 23m in R can be reached within 900s.

For the spectroscopic observations it is possible to used masks with circular holes of  3" projected diameter in the focal plane of the telescope. These masks can be produced directly from the CCD images using a computer controlled drilling device. In addition to the object holes each mask contains holes producing spectra of the sky background near the objects. Alternatively, a slit mask can be inserted in order to perform normal long slit spectroscopy. The spectra are oriented in E-W direction.

Two different grisms giving reciprocal linear dispersions of 250Å/mm and 360Å/mm, respectively, are available. For the position of the long slit, the spectral intervals covered are 4000-7200 Å and 4200-8800 Å, respectively. With a hole diameter of 3" the spectral resolution    is about 13 Å and 18 Å, respectively, i.e. a resolving power of  at central wavelengths.

Tests showed that with these standard stars a spectral classification with an accuracy of better than 5 subclasses can be obtained for objects brighter than about V= 19m with 40min exposure time. Therefore, even the optically faintest X-ray luminous coronal emitters in the, INAOE-LSW project, subsample were identified with LFOSC. Counterparts with emission lines, as e.g. AGN, can be identified as faint as  to V=21m.

The layout of LFOSC is shown below.



The CCD detector of the LFOSC is an EEV P8603 chip of format 400x600 pixels. The device specifications are tabulated below.

EEVP8603  Device Specifications
Pixel size 
Operating temperature
Bias Mean level
21 ADU 
Gain/Noise measurements
Software gain  Gain (e-/ADU)  RON (e- /pix) 
4X (default)


The quantum efficiency curve for the EEV P8603 chip is shown below:

Data acquisition and storage

The PC that controls CCD is equipped with a DAT and an EXABYTE drive. Backup of the images is done through the software  available in the PC by selecting the correct option on the shell. The data are stored in fits format. In order to read them on the Workstation, it is necessary to used procedures developed by Serrano(ping), these are BAJANOM and RENOM.

Grisms available

Grisms details
lines/mm  Interval covered wavelength (Å)  Dispersion (Å/pixel)  Resolution (slit)



      The filters available are B, V, R, I and Halpha. These filters are controlled by the same box that  controls      holmasks and calibration lamps.

Observing Strategies

Calibration Frames

Guiding Camera

Intensified CCD camera

A field of 4' X 4' north from the field of the object can be imaged and displayed in real time on a TV monitor for finding a convenient star for guiding purposes. There is a gradient on the brightness on the monitor, in order to find a star on the darker side, it is convenient to change the contrast of the screen. The guiding cross box should be with the coordinates display at the lowest level of brightness, because there is a resistance that heats up and produces that the guiding cross on the monitor blinks or distorts.

Calibration and Efficiency

            A complete sensitivity curve for the grisms available at the telescope will be posted in this page shortly (hopefully!)

AB magnitude that gives 1 ADU/s/Å at standard gain (4? e-/ADU)
Wavelength (Å) AB mag 



Examples of observations obtained with LFOSC are shown:

R band image of the field around the X-ray source RXJ1207.7+3148. The 90% SASS error circle (radius 35tex2html_wrap2797 ) is indicated. Many faint and diffuse objects, most likely distant galaxies, are visible. The brightness of the faintest visible objects is R~23. For the two brightest objects near the source position, designated by "A'' and "B'', spectra were obtained. The remaining objects are too faint for spectroscopy. Object "A'', whose spectrum is shown in the lower panel, appears to be a galaxy with R~ 20.3m and B~ 22.3m. Absorption features most likely due to MgI b and NaI D with a redshift of z~0.23 are visible. Residuals of the night sky lines are marked by "ns'', "x'' is a cosmic. Object "B'' is a 16th magnitude F-type star. This star is visually too faint to be a plausible counterpart. On the B image no object brighter than about 22tex2html_wrap_inline2703 was visible making a QSO as counterpart unlikely. The galaxy "A'' is visually too faint to be a plausible counterpart of the X-ray source . Hence, the most likely identification of this X-ray source is a distant cluster of galaxies
R image of the X-ray source RXJ0747.3+6822. The 90% SASS error circle is indicated (radius 44" ). With two exposures spectra of all objects within 60" radius around the RASS position could be obtained. "r'' denotes reflex images of bright stars in the field. In the lower panel the spectrum of object "A'' is displayed which is the likely counterpart of the RASS source. It is a Sy 1 galaxy with V~ 18m at redshift z = 0.120
R image of the position of the X-ray source RXJ0403.5+0837. In the the 90% SASS error circle (radius 44" ) several possible candidates for the optical counterpart are visible. The objects observed spectroscopically are designated by S1, "2'', "5'', and "8''. The bright object S1 is a 13th magnitude G to K-type star. Object #5 with V~18.4tex2html_wrap_inline2723is a QSO with Htex2html_wrap_inline2725+[OIII ] and MgIItex2html_wrap_inline2727 at redshift z = 0.589. Htex2html_wrap_inline2731 partly falls into the atmospheric band at 7600Å. Each of the two objects could be the X-ray source or at least contribute to the observed X-ray flux (see text). The remaining objects are faint stars which can be excluded for being the counterpart of the X-ray source

Other sources

        For more information you can consult the following:

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Maintained by Raúl Mújica Last Updated: 8Oct2000