Petra Böhm

p3d: a general data-reduction tool for fiber-fed integral-field spectrographs

The reduction of integral-field spectrograph (IFS) data is demanding work. Many repetitive operations are required to convert raw data into, typically, a large number of spectra. This effort can be markedly simplified through the use of a tool or pipeline, which is designed to complete many of the repetitive operations without human interaction. Here we present our semi-automatic data-reduction tool p3d, which is designed to be used with fiber-fed IFSs. Important components of p3d include a novel algorithm for automatic finding and tracing of spectra on the detector and two methods of optimal spectrum extraction in addition to standard aperture extraction. p3d also provides tools to combine several images, perform wavelength calibration and flat field data. p3d is at the moment configured for four IFSs. To evaluate its performance, we tested the different components of the tool. For these tests we used both simulated and observational data. We demonstrate that a correction for so-called cross-talk due to overlapping spectra on the detector is required for three of the IFSs. Without such a correction, spectra will be inaccurate, in particular if there is a significant intensity gradient across the object. Our tests showed that p3d is able to produce accurate results. p3d is a highly general and freely available tool. It is easily extended to include improved algorithms, new visualization tools, and support for additional instruments. The program code can be downloaded from the p3d-project web site http://p3d.sourceforge.net.

GRB 060605: multi-wavelength analysis of the first GRB observed using integral field spectroscopy

The long and relatively faint gamma-ray burst GRB 060605 detected by Swift/BAT lasted about 20 sec. Its afterglow could be observed with Swift/XRT for nearly 1 day, while Swift/UVOT could detect the afterglow during the first 6 hours after the event. Here, we report on integral field spectroscopy of its afterglow performed with PMAS /PPak mounted at the Calar Alto 3.5 m telescope. In addition, we report on a detailed analysis of XRT and UVOT data and on the results of deep late-time VLT observations that reveal the GRB host galaxy. We find t hat the burst occurred at a redshift of z=3.773, possibly associated with a faint, RC = 26.4± 0.3 host. Based on the optical and X-ray data, we deduce information on the SED of the afterglow, the position of the cooling frequency in the SED, the nature of the circumburst environment, its collimation factor, and its energetics. We find that the GRB fi reball was expanding into a constant-density medium and that the explosion was collimated with a narrow half-opening angle of about 2.4 degrees. The initial Lorentz factor of the fireball was about 250; however, its beaming-corrected energy release in the gamma-ray band was comparably low. The optical, X-ray afterglow, on the other hand, was rather luminous. Finally, we find that the data are consistent withi n the error bars with an achromatic evolution of the afterglo w during the suspected jet break time at about 0.27 days after the burst.

Spatially resolved spectroscopy of planetary nebulae and their halos , I. Five galactic disk objects

Strong mass loss off stars at the tip of the asymptotic giant branch (AGB) profoundly affects properties of these stars and their surroundings, including the subsequent planetary nebula (PN) stage. With this study we wanted to determine physical properties of mass loss by studying weakly emitting halos, focusing on objects in the galactic disk. Halos surround the, up to several thousand times, brighter central regions of PNe. Young halos, specifically, still contain information of the preceeding final mass loss stage on the AGB. In the observations we used the method of integral field spectroscopy with the PMAS instrument. This is the first committed study of halos of PNe that uses this technique. We improved our data analysis by a number of steps. In a study of the influence of scattered light we found that a moderate fraction of intensities in the inner halo originate in adjacent regions. As we combine line intensities of distant wavelengths, and because radial intensity gradients are steep, we corrected for effects of differential atmospheric refraction. In order to increase the signal-to-noise of weak emission lines we introduced a dedicated method to bin spectra of individual spatial elements. We also developed a general technique to part the temperature-sensitive oxygen line [O iii] λ4363 from the adjacent telluric mercury line Hg λ4358 – without using separate sky exposures. By these steps we avoided introducing errors of several thousand Kelvin to our temperature measurements in the halo. For IC 3568 we detected a halo. For M 2–2 we found a halo radius that is 2.5 times larger than reported earlier. We derived radially densely sampled temperature and density structures for four nebulae, which all extend from the central regions and out into the halo. NGC 7662, IC 3568, and NGC 6826 show steep radially increasing temperatures and a hot halo, indicating that the gas in the halo is not in thermal equilibrium. M 2–2 shows a larger temperature in the central region and an otherwise constant value. From the density structures we made estimates of core and halo masses and – for the first time reliable – mass loss rates at the tip of the AGB. All four objects show inwards radially increasing mass loss rate structures, which represent a rise by a factor of about 4–7, during the final mass loss phase, that covers a time period of approximately 10 4 years. Within a factor of two, the average of the maximum mass loss rates, which are distance dependent, is u [%]

Science verification results from PMAS

PMAS, the Potsdam Multi-Aperture Spectrophotometer, is a new integral field instrument which was commissioned at the Calar Alto 3.5 m Telescope in May 2001. We report on results obtained from a science verification run in October 2001. We present observations of the low-metallicity blue compact dwarf galaxy SBS0335-052, the ultra-luminous X-ray Source X-1 in the Holmberg II galaxy, the quadruple gravitational lens system Q2237+0305 (the “Einstein Cross”), the Galactic planetary nebula NGC7027, and extragalactic planetary nebulae in M31. PMAS is now available as a common user instrument at Calar Alto Observatory. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Faint object 3D spectroscopy with PMAS

PMAS is a fiber-coupled lens array type of integral field spectrograph, which was commissioned at the Calar Alto 3.5m Telescope in May 2001. The optical layout of the instrument was chosen such as to provide a large wavelength coverage, and good transmission from 0.35 to 1 μm. One of the major objectives of the PMAS development has been to perform 3D spectrophotometry, taking advantage of the contiguous array of spatial elements over the 2-dimensional field-of-view of the integral field unit. With science results obtained during the first two years of operation, we illustrate that 3D spectroscopy is an ideal tool for faint object spectrophotometry.

Overcoming Systematic Errors in the Spectrophotometry of Extragalactic Planetary Nebulae with 3D Spectroscopy

Using H α Fabry-Perot images of the central 7 arcmin of M31 we demonstrate the amount of filamentary gaseous emission of the ISM in the bulge of this galaxy, which, along with the high surface brightness in the continuum, is known to cause serious problems for the spectrophotometry of PNe in this region. From pioneering work in the Magellanic Clouds and M31 the observational difficulties have been known for some time. We present first observations of PNe in the bulge of M31 obtained with Integral Field Spectroscopy (3D) , a method which is shown to be capable of providing superior background subtraction accuracy, compared to conventional slit spectroscopy. Data were secured with MPFS at the Selentchuk 6m telescope, and during a commission run of PMAS at Calar Alto. It is shown how the spatial information obtained from the 3D technique is used to correct for systematic errors in the measurement of emission line intensities which have been reported in the literature.

Crowded Field 3D Spectroscopy — The Next Step: First Light for PMAS

8–10m class telescopes, combined with highly efficient instrumentation and superb seeing conditions, have set new frontiers not only for the observation of faint galaxies in the distant universe, but also for the spectroscopy of stellar populations in nearby galaxies, such as A- and B-type supergiants, luminous blue variables (LBVs), planetary nebulae (PNe), H II regions etc., which have been hardly observable with previous techniques. The detailed study of these individual objects provides information for star formation and evolution, stellar populations, chemical abundances, and hence important constraints for galactic evolution and cosmology (see also Prieto, these proceedings).